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Byepaths of Colour 
Photography 


laser 1h ARIE: 


Edited and with an Introduction 
by 
Weel AM «GAMBLE 
PO S:, 5 Wakes. 


NEW YORK: 
Peer TON & COMPANY 
681 FIFTH AVENUE 


Made and Printed in G ae ta 


HUMPHRIES & CO., LT 


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CONTENTS. 


AUTHOR’S PREFACE 

THE EDITOR’S INTRODUCTION ; 

THE DAWN OF THE ONE-EXPOSURE GAMERS 

THE EARLY ONE-EXPOSURE CAMERA 

THE CHROMOSCOPE 

REAL INVENTIONS 

REFRACTION 

PRISM SEPARATION 

EXCENTRIC PROJECTION 

DOUBLE REFLECTIONS 

INCORRECT REFLECTIONS 

CURVED SURFACES 

SOME COMPENSATIONS : 

BENNETTO’S SYSTEM AND COMPENSATION 
COMPARATIVES AND ANOMALISM IN REFLECTOR CAMERAS 
ADDITIVE AND SUBTRACTIVE LIGHT PROJECTION 
CoLouR ENIGMAS 

ADDITIVE versus SUBTRACTIVE 

FILTER ARRANGEMENT 

LIGHT FILTERS : THEORETICAL 

MAKING OF LIGHT FILTERS a 

PLATES FoR ONE-EXPOSURE CAMERAS .. = 
CoLourR SENSITIZING oe a ni ie 
CORRECT COLOUR REPRODUCTION a e x 
BALANCING OF FILTERS AND PLATES .. 

EXPOSURE 

LABORATORY Ay 

CAMERA CONSTRUCTION 

VERIFYING THE Focus 

PROCESS FAKING 

DIAPOSITIVES 

THE GREY PRINTING PLATE 

LANTERN SLIDES IN COLOUR 

BLUE TONING 

CARBON PRINTING 

CARBON TRANSFER 

CINEMATOGRAPY IN COLOURS 

KINO-STEREOSCOPY 





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AUTHOR’S PREFACE 


AUTHOR’S PREFACE, 


HOTOGRAPHY in colours has now been taken up as a 
Be in of leading interest. In this new sphere the one-ex- 

posure camera is, or has been, declared a desideratum. It 
was first suggested by Ducos du Hauron in December, 1874, but 
scored its first practical victory not with the subtractive method, or 
method as applied to printing, but with a viewing instrument for 
the additive method of colour photography, called by the maker 
the Chromoscope. 


I hope in the subsequent pages of this book to show how 
certain defects of the early inventions can be removed and a simplified 
instrument developed, so that the corrected One-exposure Camera 
may ultimately be a useful one in the hands of the subtractive colour- 


worker. 


In a general way it is only for the subtractive method that I 
have compiled these notes, which are based on my own practical 
experience, and I have refrained from using the “ additive”? method 
of inserting ‘‘ cuttings ” from other sources as my own ideas. 


Before I give a description of my own system, I think it but 
right to throw sidelights on some fallacies which have prevented, 
and still prevent, the use of the additive Chromoscope as an instru- 
ment for the substractive method of colour photography, so enabling 
others to avoid them, and also to enable them to form their own 
opinions on the different systems. All things considered, it must 
be an advantage all round to know these fallacies for technical reasons, 
as well as from the historical point of view. 


COLOUR PHOTOGRAPHY 


The various chapters were written at different times and were 
intended for separate publication, hence certain repetitions, which, 
on deciding to issue in book form, I may not have eliminated. 


When I offered my manuscript to Messrs. Penrose, Mr. W. 
Gamble agreed at once to undertake the supervision of the thoughts 
I had laboriously put to paper. I am, however, not sure in my mind 
who should be more obliged to him for this self-imposed task, the 
reader or myself. I find that he has not substantially altered the 
matter nor revised it so as to hide my independence. If the reader 
or critic finds something or other to find fault with in what I have 
written, it must unreservedly be put to my account. I have a lin- 
gering hope that some portion of my work, in this special branch of 
photography, will be of use, and that such acknowledgment will also 


be a recompense to my mentor. 
O. REG. 


Vi. 


THE EDITOR’S INTRODUCTION 


THE EDITOR’S INTRODUCTION. 


devoted many years of his life to the study of colour photo- 

graphy, but having been mainly engaged in assisting others 
to work out colour problems he has not obtained the credit of pub-. 
licity for his ideas, which include numerous ingenious forms of 
colour cameras displaying considerable ingenuity of thought. He 
has not confined himself to putting his ideas on paper, but has con- 
structed many intricate models of colour cameras with his own 
hands and has tested them thoroughly. The opinions he expresses 
in this book may, therefore, be relied upon as practical. That he 
has not been able to carry out his inventions in a commercial way, 
owing either to lack of opportunity or means, should not detract 
from their value. 


‘Lew author of this work is a practical photographer who has 


When the manuscript of the present book was submitted for 
consideration with the view to publication, it was seen to contain a 
good deal of information on methods of colour photography which 
would prove extremely useful to those who are working in this field, 
or to those who might contemplate taking up the study of the subject. 
The danger which besets experimenters in colour photography is 
that they may be unconsciously led, through lack of knowledge of 
what has been done before, into bye-paths which have already been 
well trodden by previous experimenters and proved to lead in no 
useful direction. This book will certainly prevent that, if carefully 
perused, and will indicate some of the best ways of procedure, be- 
sides furnishing such material for thought as may guide the would- 
be inventor of colour cameras or colour processes towards some 
valuable discovery. There is still a wide field for research in colour 
photography, as, although the principle has been established, many 
problems remain yet unsolved. 


Perhaps the one fault that may be found with the book, is that it 
does not cover the whole range of the subject, nor does it go into the 
underlying theories of colour work. But the author has specialized 
in a certain branch of the subject where he thought there was the 


Vil. 


COLOUR PHOTOGRAPHY 


greatest promise of success; he has dealt only with the methods 
he has himself worked and is thoroughly cognisant of, and this 
makes the book all the more valuable. 


It will, perhaps, be helpful to the reader if in this introduction 
we outline the history and the development of the three-colour 
theory, indicating some of the methods which have gone beyond the 
experimental stage and have been brought more or less into use. 


Disregarding the efforts made by scientists, even before the 
invention of photography, to fix the colours of the spectrum on 
chemically-prepared surfaces we must give credit to Louis Ducos 
Du Hauron, a Frenchman, for the invention of three-colour photo- 
graphy as we now generally understand it. His work dates from 
1859 when he foreshadowed this process in a paper read before a 
French scientific society. This was followed by fuller publication 
of his idea in 1862 when the photographic reconstitution of colours 
was clearly defined. In 1869 Du Hauron published the first hand- 
book of photography in colours, in which he described all essentials 
for success with the process. 


One of Du Hauron’s suggestions was to place three sensitive 
surfaces one behind the other like the leaves of a book and make one 
exposure through them in an ordinary camera. He predicted that 
this method, which he calls the dialytic system, would in the end 
supersede all three-colour systems. It should be noted, therefore, 
that it is upon a modification of that method the author of the present 
work pins his faith as the process most likely to give successful 
results. 


Mr. F. E. Ives, a most prolific inventor of three-colour cameras 
and methods, seems to have arrived at a similar conclusion, for his 
latest method appears to be based on the same idea. 


Whilst we give credit to Du Hauron for the earliest publication of 
the three-colour idea it is but fair in the interests of historical ac- 
curacy to also mention the work of James Clerk Maxwell, who had 
apparently been working on the problem without knowledge of 
Du Hauron’s efforts. Lecturing at the Royal Institution in 1860, 
Maxwell indicated the possibility of three-colour heliochromy, and 
gave a demonstration in support of his theory. 


Vill 


THE EDITOR’S INTRODUCTION 


But after all both Du Hauron and Maxwell no doubt based 
their ideas on the three-colour vision theory proposed by Dr. Thomas 
Young. According to his conception the human vision is tri- 
chromatic, and the fact that most hues could be imitated by three 
pigments strengthened the conclusion. This theory was subse- 
quently amplified by Professor Helmholtz. Du Hauron applied 
it practically to photography, whilst Maxwell was attracted to it asa 
scientist and proceeded to support it by careful quantitative ex- 
periments, using photography as a means of demonstrating his 
conclusions. 


The leading idea of these early experimenters was that if the 
eye can see only three colours and forms the other colours of the 
spectrum by admixture, then the lens of the photographic camera, 
replacing the eye, must likewise take in these three colours, and the 
photographic plate is the equivalent of the retina. Thus they 
argued that if these three colours could be taken one at a time on 
three separate plates, and the images subsequently reconstituted 
by projecting them from a lantern or by printing them one over the 
other on paper, we ought to get a fair imitation of the colours of 
nature. 


The basis is thoroughly sound, but the difficulties of carrying 
out the theory have proved very great. To begin with it was found 
that the ordinary photographic plate was more sensitive to the blues 
and violets than to the green, yellow and orange parts of the spectrum. 
Maxwell pointed out this difficulty and suggested that if photo- 
graphic plates more sensitive to these last-named colours could be 
found the results would be improved. There were no colour- 
sensitive plates in those days, and it was not evident how this diffi- 
culty could be overcome until 1873 when Professor Vogel announced 
that the impregnation of the sensitive film with dyes would influence 
the distribution of colour-sensitiveness in the photographic plate. 
Du Hauron grasped the importance of this discovery at once, and in 
his French patent specification of 1874 he mentioned the use of 
colour-sensitizing dyes. This was elaborated in his English patent 
of 1876. 


Given the colour-sensitive plates the next part of the problem 
to solve was the preparation of suitable colour filters so that only 


1x. 


COLOUR PHOTOGRAPHY 


light of the particular colour desired should reach the plate at each 
exposure. This did not prove a very easy matter. The scientist 
was able to say what the colours of the three respective rays should 
be, but it was very difficult for the practical man to find suitable 
coloured glasses or dyes to form coloured films which would pass 
these rays, and even now the problem cannot be regarded as fully 
solved. It is accepted that the light-filters for taking should be red, 
green and blue-violet, but there can be a wide difference in the 
conception of these colours according to the materials used for pro- 
ducing them, and only by careful spectroscopic tests can we obtain 
an approximation of what is best. 


Having obtained the plates and the filters, the inventors in this 
field, from Du Hauron onwards, set to work to devise cameras 
which would form the images successively or simultaneously. It 
is quite easy, of course, to take three images successively in an 
ordinary camera, changing filters and plates as rapidly as possible, 
but such a method will only be successful when taking inanimate 
objects, and where there is no possibility of the light changing 
rapidly. The great desideratum was therefore to make the ex- 
posures simultaneously, and here is where numerous experimenters 
have exercised their ingenuity, as the subsequent pages of this book 
wil] show. 


The difficulty is to get the three images exactly the same size 
and with the same perspective so that they can be exactly super- 
imposed. That result has been achieved, but whether by the best 
means for commercial application remains to be seen. Separating 
the images by mirrors or prisms has been found full of snares and 
pitfalls, besides necessitating elaborate and expensive construction 
in the cameras, with corresponding probability of the apparatus 
getting out of order. 


If we can eventually realize Du Hauron’s idea of placing the 
sensitive surfaces one behind the other, with the colour filters be- 
tween, like the pages of a book, and use the colour sensitive “ film 
pack ” in an ordinary camera the method would be ideal. Before 
that can be accomplished much will have to be done by our dry- 
plate and film manufacturers. They must give us thin sensitive 


xX. 


THE EDITOR’S INTRODUCTION 


films of the greatest translucency and sensitive to exactly those por- 
tions of the spectrum we want to record on each of the three sur- 
faces. The absorption of the uppermost films will have to be al- 
- lowed for both in the general and colour-sensitiveness, and will 
have to be controlled or supplemented by adjustment of the inter- 
posed colour filter films. How far these things are likely to be 
accomplished can be better judged when the reader has gone through 
this book. 


Of course, when we have got the colour negatives right there 
remains the final problem, perhaps the greatest of all, as to how to 
obtain the coloured prints from them. As the author shows there 
are various ways of doing this, and many other ways have been 
suggested which the author has not thought it worth while to des- 
‘cribe because he has not worked them. 


In the opinion of the writer of these remarks there should not 
be much difficulty in applying the ordinary methods of colour 
printing—such as by half-tone blocks, photogravure, collotype or 
photo-lithography—to the reproduction of good three-colour record 
Negatives, indeed the means exist now. The negatives must, how- 
ever, be good in three essentials. They should be equal in size and 
perspective, should correctly record the colour effect, and have 
equal photographic density. Most negatives produced by three- 
‘colour cameras so far have been sadly lacking in one or other— 
and in some cases in all—of these qualities. In these directions im- 
provement must be sought before we can hope to see really successful 
colour printing, whatever may be the process employed. 


The process block-maker can as a rule bring about a good 
result even from an imperfect set of negatives, but he ought not to 
be expected to do this, and it lays him open to the charge of “‘ faking ” 
the result. Some amount of manipulative skill in the direction of 
what is called “‘ fine etching” is necessary with half-tone block 
making, but this should only be for the purpose of correcting the 
inherent limitations of the process in regard to tone rendering, not 
to correct faulty three-colour records. 


In the case of photogravure, collotype and photo-lithography 
(especially by graining methods), there is not so much scope for 


a 


COLOUR PHOTOGRAPHY 


“‘ faking,’ and first-class original negatives are essential. Given 
such negatives there are wonderful possibilities for three-colour 
printing by these processes, and we may look for the greatest develop- 
ments along this line. 


As regards colour prints by photographic or semi-photographic 
methods it will be seen that the author has the greatest faith in the 
carbon process, and if some of its difficulties could be overcome— 
such as those due to stretching of the paper, and the somewhat im- 
perfect pigments which are used in the tissue—there would be great 
hope for this method. Processes of using dyed films require a good 
deal of manipulative skill, and so do methods of toning bromide 
prints. In fact a really good, easy and reliable process for colour- 
print making has yet to be evolved. Perhaps the information on 
the method of producing three-colour negative records as a basis 
for reproduction as given in this book may point the way. 


It may be noted by those who are familiar with the various 
methods of three-colour work in vogue up to the present day that 
nothing is said about such processes as Autochrome, Paget, Dufay, 
Omnicolore, etc. These belong to a different category than the 
methods which the author has sought to expound, and it would 
necessitate a much larger book to deal with them. Moreover it 
would be likely to confuse the reader to deal with too many alternative 
methods of carrying out the three-colour principle. Information 
about such processes can readily be found in other books. 


In the present work the opportunity is given to the reader to 
study very thoroughly one of the most important paths in three- 
colour photography. The course chosen may prove only a bye- 
path, indirectly leading to some epoch-making discovery, or it may 
widen out into a clear and direct way to successful three-colour 
photography. 

WILLIAM GAMBLE. 


X11. 


THE DAWN OF THE ONE-EXPOSURE CAMERA I 


CUS bAWr TMD IRS alle 


THE DAWN OF THE ONE-EXPOSURE 
CAMERA. 


colours by photographic means, excluding all handwork, was 

born with the photographic process. To give the different 
dates of history appertaining to the applicative development of this 
new idea for art and craft would be a long story, but an abridged 
historical note, based on patent-records, may be of general interest. 
It is the part least known. 

Photography in natural colours is, as a whole, divided into two 
main methods: the additive and the subtractive method. 

The additive method of colour definition is the younger branch, 
but is nevertheless now considered the foundation on which are 
based the modern scientific explanations, and from which deduc- 
tions are made in respect of light, its composition, and its separation 
into the prismatic colour rays. It is generally agreed that the 
additive primary colours into which white light can be separated by 
passing through dispersing prisms, are violet, green and orange. 
If these primaries are again united by three light projections, white 
light is formed by the amalgamation. 

The union of green and orange light alone would form yellow 
light. If we desire to have a blue light we have to superpose green 
and violet rays, and orange and violet would show as pink when 
united. 

The additive method is the base for the chromoscopic and 
kinematographic colour projection. The Autochrome and similar 
one-plate colour-photographic productions are effected by what 
may be described as a semi-additive method. 

The older method of colour definition is the subtractive method, 
and is the one which shows the results by reflected light ; the three 
subtractive primary or printing colours are blue, yellow and pink, 
and these three colours when superposed form black. To show the 
desired colours on the image, we have to subtract, that is to say, we 


4 pas attempt to solve the problem of producing pictures in 


2 COLOUR PHOTOGRAPHY 


take away the colours not desired. If we omit to print pink, but 
print only yellow and blue in superposition or as mixture, we produce 
green or a colour minus pink. (Pink is often called red, a name that 
is just as often given to dark-orange, the special red). 

The combination of pigments and the whole scale of such 
colours is known to us, and has been used since painting and printing 
became the means employed for embellishment in our homes and in 
developing art and industry. It is the same to-day when applied 
to photographically selected colour records. 

The first suggestion to use photographic means for making colour 
representations by photographic colour selection, as embodied in a 
patent, comes from Ducos du Hauron;* his first English Patent, 
2,973 issued 1876, shows him as father of nearly all colour cameras, 
and his directions for colour printing are still used to-day. His 
specification of 17 pages can even now be had at the Patent Office, 
price I/-. . 

Later inventors have too often neglected to mention, that their 
wisdom was derived from the teachings of Ducos du Hauron, and 
some have even denied certain facts, found in black and white in the 
patent specification mentioned above. Some abstracts from this 
document should therefore be welcome, especially the one which 
quotes the suggested One-Exposure Camera. Page 15, part 9 says: | 

“9g. Principles of Construction of a Triple Camera 
adapted to the system. Simultaneous and lineal identity of the 
proofs. 

‘“‘ The rays coming from the subject to be reproduced are 
received upon a glass unsilvered with parallel faces inclined 45°, 
or thereabouts, in respect to the model and in respect to a first 
lens, towards which it reflects a part of the above-mentioned 
rays. The greater part of these rays traverse this first glass, 
and they are received by a second glass equally unsilvered and 
with parallel faces also inclined 45°, or thereabouts, in relation 
to the model and in relation to a second lens towards which it 
partially reflects the rays which it receives. Lastly, the rays 
that this second glass allows to pass are received by a third lens 
either direct or by interposing a silvered or metallized glass 
which reflects nearly all of them. 





*Du Hauron died on the 31st August, 1920, in extreme poverty, at the age 
of 83. He never really profitted by any of his numerous clever inventions in 
three-colour photography. 


THE DAWN OF THE ONE-EXPOSURE CAMERA. 5 


“In virtue of this arrangement the three images received 
by the three lenses are geometrically the same. 

“There are evidently many ways of varying this con- 
struction without departing from the essential elements thereof, 
and which I have specified.” 

Ducos du Hauron does not specifically repeat that light-filters 
have to be inserted in the different light-paths of this triple camera, 


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Green Filter 


Orange Filter 
Fa 


Fig. 1.—Ducos du Hauron, English Patent 2973/76. 
O, First mirror 
P, Second mirror. 


but speaking in a general way, how the negative colour records 
have to be taken in any colour camera, he says (page 4) : 

“as to defining for its practical operation the course of the 

manipulations one may say that they consist: Firstly—In 

producing in the camera three negatives of the same subject, 
one by green light, the second by orange light, the third by 

violet light. , 
and page 10, what we now describe as light-filters are referred to 
as the 

‘“*‘ manufacture of three sorts of glass or coloured mediums.” 

I have made a drawing of the one-exposure camera described, 
believing it to be a great help to better understand Ducos du Hauron’s 
directions. (Fig. 1). The position of the light filters I take to be 
interchangeable. 


4 COLOUR PHOTOGRAPHY 


CHAPTER’ Lh: 


THE EARLY ONE-EXPOSURE CAMERA. 


INCE writing my last chapter, I found that Ducos du Hauron’s 

triple camera was patented before 1876, in France on December 

15, 1874, and is there registered under Number 105,881. The 
complete patent specification shows clearly that all his cameras were 
intended for the subtractive method only, because different methods 
are given, how to print from the negative colour records in super- 
position or by pigmentary colours, and no reference whatever is made 
therein to the additive method of colour photography, that is, to 
glass positives viewed in an instrument in which the light-cones are 
coloured by selective light-filters. 









‘lq. UeedH 


Fig. 2.—A. H. Cros, English Patent 9012/89. 


Antoine Hippolyte Cros, physician, of Paris, patented in England, 
1889,—registered under Number 9,012—a triple camera, indicating 
the same plainly for the additive method only, a system which is now 
known as the Chromoscope, a viewing instrument pure and simple. 
If Cros did not invent the name ‘“‘ Chromoscope,”’ but only des- 
cribed the action of such an instrument, it could not possibly be a 
reason for withholding from him the acknowledgment that he is the 
originator, and not a later-comer. 


THE EARLY ONE-EXPOSURE CAMERA 5 


Cros’s Invention seems to have been premature, and little is 
known of his work. It was quite by chance that I came across his 
patent application, applied for in England under his patent agents’ 
name, of which specification I give an abridgment. The drawing 
(Fig. 2) will explain itself, and it is not necessary to point out the 
weakness of the system for taking the negatives. I, however, draw 
attention to the possibility that positives, the negatives for which are 
obtained by three separate exposures by an ordinary camera, can be 
shown; and further, if the internal transparent reflector “‘P” is 
elongated, so that the last light-cone ““ CR3” has also to pass through 
glass of the same thickness as the others, all the three pictures 
being refracted alike, we have a fully compensated triple viewing 
camera (as good as any others invented afterwards), in so far that the 
irregularities imparted by refraction would be alike in all three 
picture-paths. The specification says :— 

‘“‘ Negatives are produced from the action of orange, green and 
violet light respectively. Positives are printed from the nega- 
tives, and to reproduce a picture they are introduced into the 
grooves for the sensitive plates of the camera behind the coloured 
glasses. Light being admitted from behind, the images may be 
seen through lens combined.”’ 

Our next enlightenment in respect of triple cameras is found in 
Patent Specification 4606/92 (U.S.A. 475084), the subscriber to 
which is F. E. Ives, and the abridgment says : 

“* Camera for producing Multiple Pictures showing the same 
perspective, the incident rays are allowed to fall on a (trans- 
parent) mirror O, which reflects some and transmits the re- 
mainder. The reflected and transmitted rays are again re- 
flected and transmitted by an arrangement of reflectors and 
mirrors, until ultimately the rays are reflected from the re- 
flectors (prisms) to the sensitized plates to produce three dis 
tinct and similar pictures. The camera also serves to super- 
pose the several images by vision in a transmitting camera. 

The complete specification has several illustrations, one of 
which resembles the drawing shown for Ducos du Hauron’s des- 
cribed arrangement. The difference lies in that right-angle prisms 
are as a new element inserted at the three places marked “ Pr” 
(as illustrated by the smaller side-drawing of Fig. 3); each prism 
is followed by a lens. No ocular lens, however, is used in this case, 
but instead a special ocular mirror inclined at 45° is substituted. 


6 COLOUR PHOTOGRAPHY 


This formation throws the three pictures all on one plane, so that one 
slide will do, instead of three as before, and it is also suggested that an 
ordinary camera could be adapted, the prisms, lenses and reflectors 
being fitted on a lens board. 





Fig. 3.—F. E. Ives, English Patent 4606/92. 


My drawing (Fig. 3) gives one formation of the invention : 
““O” and“ P” are the transparent reflectors; sands. see sie 
ocular lens (or ocular mirror) which projects the light-rays by re- 
flection and refraction, in this case, to the three focussing planes. 
Other variations of this one ocular system are suggested by inserting 
some more transparent reflectors. 

A similar instrument to that shown in Fig. 3, omitting the 
prisms and internal lenses, was also formed, having three different 
focussing planes, and only one lens, which gives me the opportunity 
to make the following critical observation, that is, the light-rays 
do not only pass as shown by the central ray, but the light derived 
from spaced objects on view is projected by a lens in the form of a 
light-cone, the diameter of which becomes larger the further away the 
focus distance is from the lens. The tangent “ T ” is such an ex- 
ternal ray of a light-cone which is spreading some light on a focussing 
plane, where only reflected light should arrive. This extraneous 
light on focus “‘ Fr ”’ would not allow the three pictures to be taken 
faultlessly by simultaneous exposure. 

There is another item. In 1892 there were no colour-sensitizers 
known which allowed such a rapid exposure for the red end of the 
spectrum as to permit a simultaneous exposure. 

T he negatives in such instruments have therefore to be taken 
by other means, that is, in a direct-vision camera, permitting three 


THE EARLY ONE=-EXPOSURE CAMERA 7 


separate exposures in the same focussing-plane. On the other hand, 
if the light enters the instrument through the three focussing planes, 
illuminating the three glass positives as suggested by Cros, then no 
false light can disturb the amalgamation by sight, of the three pictures, 
into one when observed at the union point of the three light-cones, 
the one ocular lens. 

Strange to say the patent specification 4606/92 does not describe 
or claim any connection with colour photography, and does not say 
that the three pictures are taken or shown by inserting light-filters, 
but the construction of such a triple camera cannot be for any other 
purpose, and in later years has been declared, as the complete solution 
of colour photography by the additive, as well as the subtractive, 
method. Later inventors, however, have proved that finality in 
this respect has not yet been reached. 

The Inventions patented by White 8663/96, 18875/98, and 
Shepherd 10993/02 are somewhat similar. 


8 COLOUR PHOTOGRAPHY 


CHA Pith bits 


THE CHROMOSCOPE 


in his patent specification, “ there are evidently many ways 
of varying this construction without departing from the 
essential element thereof.” 

In my first article I illustrated the above quoted camera, giving 
the two primary transparent reflectors ““O” and “ P” as at right 
angles, but as suggested above, the construction can be varied. By 
placing the two reflectors parallel we should, of course, not depart 
from the essential element, and still keep to Ducos du Hauron’s 
direction how to make a triple camera. 

This brings us to the next line of thought, and development 
in colour photography, a direction which has been taken by F. E. 
Ives as published in his patent specification 2305/95. (U.S.A. 
531040), where Ives says : 

“The term ‘ Photo-chromoscope’ I apply to an instru- 
ment intended to blend together, by optical means, a series of 
images of the same subject, which series of images constitutes 
what I term a chromogram, and which are seen through different- 
coloured glasses or by means of different coloured lights. 

“‘ In the present case there is a green screen, a blue-violet 
screen and a red screen. | 

** Each section of the Chromogram consists of a glass or 
other transparent plate upon which the photographic image is 
directly produced.” 

These few sentences copied from the inventor’s Patent des- 
cription, distinctly show that the invention is for the additive method 
of colour photography only, as before suggested by Cros. 

In the larger drawing of Fig. 4, the tangent “ T ” representing 
an outside light-ray of the light-cone shows the impossibility of 
using such a triple camera for taking negatives for the subtractive 
method, nor as a matter of fact for the additive method either. 

The whole invention is strictly limited to the formation of a 
viewing instrument. 


| Dies du Hauron says, when describing his triple camera, 


THE CHROMOSCOPE 9 


For this invention also, the negatives had undoubtedly to be 
taken by other means, or a camera had to be constructed in a way 
which is not explained in the patent specification. 

Several varieties of instrument are given in the same specifica- 
tion, two of which are in a small size, illustrated next to the principal 
drawing in Fig. 4, but apparatus made according to them are still 
less capable of being used for taking negatives. 





Fig 4—F. E. Ives, English Patent 2305/95. 


Referring to the larger drawing, embodying the intended in- 
vention, light-filters are inserted in the different light-paths, one 
vertical and the other two slightly inclined at about 20°. Why they 
are inclined is not disclosed in the patent specification, but in later 
years it was claimed that the slanting light-filters were really acting 
as compensators for refraction defects. This assertion does not seem 
very convincing, since we know now that such a compensation has 
to be inserted at the same angle as the reflector “ O ” or “ P,” that 
is 45° and not 20° as shown, and I suggest that the slanting to 
20° was more likely adopted for the purpose of scattering any pos- 
sible internal reflection. 

The inventions patented by Edwards 3615/95, Butler 29353 /97, 
Butler 4290/05 are on similar lines in which, with the aid of one 
lens and two main reflectors placed parallel into the camera, three 
pictures are placed in three different focussing planes. 

The patent specification 3784/95 (U.S.A. 546889) shows the 
capability of the inventor to theorize, using his faculties to evolve a _ 
highly scientific instrument “‘ on paper,” but we can take it that the 
technical difficulties to bring the apparatus into working existence 
are such that no optician or mechanic is able to overcome them. 


IO COLOUR PHOTOGRAPHY 


The inventor may have been able to make a fixed-focus instrument 
to his own satisfaction, but to manufacture such an ideal for general 
use is quite another thing. 

In this invention there is in short one ocular lens, then an extra 
lens for each of the three light paths, and countless internal re- 
flectors, the adjustment of which is an impossibility. It is also not 
possible to take negatives with this ideal. 

The patents 15753/99, 12514/03, 25142/12 are marked with 
the same defect. The last named has also a resemblance to the 
Cros patent. 

A battery of three lenses triangularly pressed together forming 
a “‘trio,”? each with a right-angle prism to throws the respective 
picture sidewards is a patented proposition of Meyer 7193/97, and 
a similar trio of lenses without the reflectors is also patented under 
14364/99 Pollock. Three lenses in a line, the light-cone of the outer 
lenses being reflected by mirrors or right-angle prisms and the 
middle light-cone compensated with the aid of an extra lens, is to 
the credit of Abney 14623/05; and three lenses on a common long- 
shaped camera body forming three joint cameras, shows a complete 
stereoscopic forgetfulness of another inventor, the name of whom 
is appended to specification 3560.99. These cameras might have 
been designed to take views from aeroplanes, an ordinary view 
with foreground being out of the question, the stereoscopic differences 
would be too pronounced and would show as colour fringes, when 
the three colour prints were superposed to form a united picture. 

As something out of the way, the chromoscope described by 
Barnard in specification 3476/02 is worth describing, it has found 
imitators without being verified as to the possibilities. This time 
the two transparent reflectors ““O” and “ P” are formed into a 
cross placed into a square box; one side carried the ocular lens and 
the other three sides are decorated with the different light-filters, 
and the respective positive colour records are placed outside. This 
invention is remarkable for its perplexities and kaleidoscopic sur- 
prises. 


tii te el 


a 


REAL INVENTIONS II 


CHAR ED Rely. 


REAL INVENTIONS 


that form the basis of educational knowledge, and on that basis 

of justification, I will now record the most impossible proposals 
made for triple cameras, as a warning to others to save them falling 
into the sameerrors. The ball was set rolling—as the saying is—in the 
States. It is, however, impossible that the inventor of this ‘ real 
invention ” verified his theory, neither evidently did his followers. 
These inventors did, however, one good thing, and only one, that 
is, they enriched the Government coffers by paying the patent fees. 

As a preliminary, I may add that Theodore Brown, in 1894, 
was granted a patent 21406/94, for a stereoscopic reflecting system, 
in which four mirrors were placed in. such a manner, in front of 
one lens, that two pictures were projected, through the one lens, to 
the focussing-plane at the back. It is not my place to theorize here 
on the merit, of this invention, but simply to say, that the idea as 
such, was perfectly sound for the aim indicated. 

For the purpose of colour photography, and the necessary 
splitting up of the view, to form three pictures, the inventors took 
hold of this same stereoscopic transmitter, or reflecting device, and 
placed the same in one form, or another, between the one lens and 
three focussing planes,to form three colour records. With the 
help of science disguised as a fairy, and an assurance worthy of a 
better cause, it was claimed for these new “ inventions” that the 
pictures were all of the same size and from the same point of view, 
and therefore not stereoscopic. 

I have no desire to commemorate the names of these imaginative 
geniuses, but I cannot abstain from giving six illustrations (Fig. 5) 
of their suggested absurdities, all of which give in each focussing- 
plane only one part of a panoramic view, and when these parts are 
again joined and superposed where necessary, we find that the three 
pictures form only panoramic part-pictures of one whole picture, 
which latter could have been taken easier, and with less trouble, with 
an ordinary lens and ordinary camera. 


|: a great measure it is the failures and not the ultimate success 


I2 COLOUR PHOTOGRAPHY 


An eminent optician, whose name is a household word with 
every photographer, thought he could do much better, made a large 
lens and by using a stop with three spaced apertures—that is, he 
created three artificial or excentric lens centres—thinking to form 
three correct pictures in three focussing planes by interposing a 
reflector behind each aperture. He showed his work at a meeting 
of a celebrated society, but the wisdom came after, he saved the 
patent fees, so the idea is still open and patentable 





Fig. 5.—Real inventions. 


Another up-to-date inventor whose speciality is Colour Kine- 
matography proposes to use three lenses, one above the other, taking 
three pictures from three different points of view, but he does not 
acknowledge that there is any stereoscopic difference between three 
pictures so obtained. At the same time he claims to be able to 
insert, ‘‘ well-known means ”’ to efface the effect of “‘ parallax,” but 
what the means are which eliminate such is not disclosed. But 
then the term “ well-known means ” found lately in many patent 
specifications, gives the person saying it, such an air of superiority, 
and if you yourself don’t know the “ well-known means ” you feel 
as if you must hide yourself for shame, in not knowing such a simple 
thing, that is well known. Between us, however, it may be stated 
that there are no means to correct stereoscopic differences. 

A new idea’ in one-exposure cameras is indicated in Patent 
28920/97. ‘This patent of Bennetto has a slight basis on Ducos du 


REAL INVENTIONS 13 


Hauron’s triple-camera. It is a one-reflector camera. The re- 
flector is a light filter, in this case an orange-red filter. One plate 
is exposed by the transmitted light and two plates forming a pack 
are exposed by the reflected light. This one-exposure, one-re- 
flector, separation camera, is to my mind, when certain defects are 
eliminated or compensated, the basis of the possible subtractive 
colour camera, de facto ; such a camera, size 12 by Io inches, has 
been used by me. 

Derivates of this idea are: Lumly 4164/99, who claims Ben- 
netto’s Camera for the additive method, and Butler 9936/99, who 
simply joins two Bennetto Cameras together to form a stereoscopic 
combination. | 

_ Davidson 10043/o1 had the idea of making the whole thing 
collapsible, a carrier, holding a falling-out reflector at 45°, and also a 
falling out plate-pack at 90°, all fitted beautifully into a slide which 
can be used in an ordinary camera; this is the culmination of sim- 
plicity. The inventor, after all, seems however not to have been 
satisfied with it, because his specification 15204/04 proposes a solid 
and adjusted Bennetto reflector box to be made attachable and de- 
tachable to an ordinary bellows camera. Pfenninger (25907/06) 
finds that it requires a refraction compensator in a Bennetto camera 
and later in 1910 (No. 26609) he proposes a self-compensating re- 
flector filter. 

The above referred to inventor, who first adapted the stereo- 
transmitter for a colour camera, has also tried to improve the Bennetto 
camera; he advises the insertion of a special lens, to render all rays 
parallel, before passing through the reflector filter, thinking there 
would be no refraction defect ; but how if you desire a 12 by Io inch 
camera? I wonder whether this “invention” has been verified. 
I defy him to find any picture-focus.. 


I4 COLOUR PHOTOGRAPHY 


CHAP Gi aye 


REFRACTION 


HEN we insert in a square box a plain glass, not surfaced 
\ \ or silvered, inclined at 45°, such a glass will act as a mirror, 
also called reflector, and if such a reflector is also a light- 
filter, ‘‘ reflector filter ’’ will be the description of the same. If now 
a light-cone by means of projected light falls on the reflector, part of 
the light-cone will be thrown upwards or sidewards, and is reflected 
towards one side of the box; and the other part of the same light- 
cone will be transmitted, or passed through the glass, to the back of 
the box. Such an apparatus having one optical centre, but forming 
two focussing planes, is the simplest form of a one-exposure camera, 
and is the invention made by Bennetto, of Penzance, in Cornwall. 

In the early times when glass positives, obtained from three- 
exposure negatives, were shown in a Chromoscope, it was found that 
the glass positives would not register. The same happened if by 
means of a Chromoscope, as first introduced, three negatives were 
taken; the negatives would not be of the same size, but a clear 
explanation was in those early times not forthcoming, and it is my 
special purpose, to demonstrate in the following lines, that it is pos- 
sible for glass, optical, flat and parallel, to introduce deformity into 
the picture, which is obtained by projecting a light-cone through 
such glass. 

The appended drawing (Fig. 6) “ Refraction through parallel 
plate ’ gives one all the optical bearings, of a glass inclined at 45°. 

The lower half shows the “ Vertical Refraction’ accumulative, 
therefore not balanced. The focus in both figures is taken as 120 
points. The central radii are 30. The glass displaces the focus 
by ten points, and it will be seen that the vertical refraction gives 
the focus-width six points short. 

If we adjust the vertical focus also to 120 points, then the focal- 
length of the horizontal refraction will be lengthened by five points. 
Without the glass a square, all sides having 120 points, will be formed. 
If a glass at right angles to the central is inserted, the same square 
is formed, only the focus is slightly displaced. No square can be 


ee ee 


REFRACTION 15 


formed if the glass is inserted at unequal angles to the central ray. 
The difference between the horizontal and the vertical transmission 
is about one-sixth part of the reflector employed, if we take the 
reflector to be the standard measure for comparison. 


Horizontal or balanced refraction. 





same plan 


be oe 





120 


F3 


As pil" Ne nae aah EEG ree Daag 


Vertical or not balanced, accumulative refraction. 


Fig. 6 —Refraction through a parallel plate inclined at 45 degrees. 


If we copy an exact square through the glass which is inclined, 
the copy will not be square, but oblong, and no shifting forwards or 
backwards, no inclination of the focussing plane, will correct the 


16 COLOUR PHOTOGRAPHY 


defect of foreshortening or pressing together of two opposed sides 
in the formed picture. This defect is generally referred to when 
spoken of as a “ refraction defect.” 

If we place the two reflectors parallel or at right angles to each 
other, as directed by Ducos du Hauron for his triple-camera, or by 







Prism Base down 


Refraction 






. 
Chhihaabahehl Lh hbbk 
— 


Prism Base up ec, | 
Vi Pe 


Refraction ao 


PC ee ot ee ee 


Fig. 7. 


Ives in his Chromoscope, or by others, we do not diminish or com- 
pensate this defect, but we multiply or increase the same, and we do 
the same with each other addition of light-filters and reflectors if 
inserted the same way as indicated above. Therefore, such cameras 
are absolutely of no use for the subtractive method of colour- 
photography, a method which requires three negative colour records 
of the same size. 


Eee 


REFRACTION 7 


Speaking of refracted pictures and displaced focussing-planes, 
I have also to allude to ‘“‘ Prism base down refraction ” and “ Prism 
base up refraction ” (Fig. 7) and the displacement of the light-cone 
such interposition is causing. The focussing planes obtained without 
refraction F 1, with parallel Plate Refraction F 3, and the re- 
fraction with the wedge F 2, are given in the drawings and show 
the difference. The focus planes are given as of same length and 
in parallel displacement. 


18 COLOUR PHOTOGRAPHY 


CHAPTER VI. 
PRISM SEPARATION 


S I have said before, it is by failures that we gain our know- 
A ledge, and they guide us to improvements. If I give some 

of the vagaries through which the early workers had to wade 
in the search for a workable one-exposure camera, the knowledge 
of these failures may still be instructive, and may well serve as a 
basis for future experts. 

It was in the beginning of 1904 that a patent was filed, in which 
by the aid of two wedge-shaped prisms placed in front of one lens, 
two identical pictures by the dispersive powers of the prisms were to 
be formed at the back of the one lens, and by the aid and inter- 
position of light-filters the negative colour records were to be ob- 
tained. My drawings show the possibilities for a camera having a 
two-picture focus only. The defects would obviously be exag- 
gerated in a formation showing how to obtain three separate pic- 
tures, so there 1s no need for me to discuss the latter case specially. 


Tae 
at ar ae 
Sai ee 
~. + 
~ 












“RR 

b eS UREA 
Toft I 
A Fe “c © b 


Fig. 8. Exterior Prism Position. 


Taking the “‘ Exterior prism position ” (Fig. 8) first, the prism 
placed as an ocular will see not less than from “a” to “e,” and re- 
fract the passing light-rays towards its base ; the axial ray from “ c ” 
will be deflected about 2/3, that is if a prism of 15° is used, the de- 
flection will be about 10° therefore one axial ray from “‘c” will be 
deflected to “‘c 1.” This formation is also liable to project ghost 
pictures, the ray ‘‘ RR 1,” from “‘e” arrives aS) k=) see 
that is, on the picture-plane, where the second prism “P 2’ 
should form the second picture. The two pictures obtained by such 


eee 


PRISM SEPARATION 19 


a formation, as to graduation, are shown in ‘“‘ F 1” and F 2,” of 
the smaller drawing and I specially draw attention to the ghost 
marked “e.’? This ghost-picture can be made less dangerous, if 
the space “a e”’ is covered with dark non-reflecting materials. 


UJ 


N 
N 
N 
XN 
N 
N 
N 
N) 
N 
N 
a 
N 
N 
N 
NY 
s 
N 
N 
N 
N 
N 
N 
N 
N 


Z 
Z 
Orrd: 





Fig. 9. Interior Prism Position. 


Instead of placing two prisms, base to base, in front of one 
lens, we can also insert two prisms, apex joining, at the back of a 
lens, between lens and focussing plane, as shown in my drawing 
“Interior prism position” (Fig. 9). This arrangement has the 
advantage, in not permitting any light-rays to transgress over the 
optical axis, which passes from “O” to “d1,” because all light- 
rays passing through such a prism and being part of a direct light- 
cone, collected and projected by a lens, will be refracted and thereby 
deflected towards the base of the prism, the formation of any secon- 
dary pictures or ghosts, on the other side of the axis, is impossible. 

In the little side drawing, the graduation imparted by the action 
of the prisms on the two pictures in focus “ F 1” and “ F 2” is 
illustrated, showing such pictures in superposition. If ‘“ F1”’ 
should represent a red picture and “ F 2” a blue picture, then, in 
the united picture, the red would predominate near “ b c,” and the 
blue near “‘c b’”’; obviously not a very desirable solution. 

In all prism systems, having wedge-shaped prisms, a certain 
want of sharpness will be imparted to the pictures, caused by the 
dispersion of the passing light-rays, and also as with all interposed 
heavier refracting material, a certain displacement of the focus 
plane will take place. 

It has been recommended to separate the prisms, so that a 
third picture between the two deflected pictures could be obtained. 
This supposed invention is defective, in that the central picture will 


20 COLOUR PHOTOGRAPHY 


be at a different focus distance, and also of different size, as compared 
with the other two pictures, and all pictures are only connected 
together by what I may call prismatic and panorama-like continua- 
tion, and I am not sure if stereoscopic differences are not present. 





There is one predominant point which puts all cameras having 
wedge-shaped prisms out of court, and that is, such cameras would 
allow the taking of very small pictures only, therefore even if in all 
other respects the negatives were satisfactory, the size would not be 
useful for the subtractive method of colour photography. 

An additional drawing (Fig. 10) shows different light-rays 
entering a prism of about 30°. After the first refraction by surface 
“Sr” each white light-ray takes a new direction for the different 
colour rays, which come to view as spectral colours, after having 
passed refracting surface ‘“‘S2.” The light-rays can also enter the 
opposite way, when the spectral colours will naturally also be seen 
the other way, but the main direction ot each light-ray would be the 
same as here given. 


_— 


EXCENTRIC PROJECTION 21 


CISUA PIMOS 2 Oe 


EXCENTRIC PROJECTION 


a lens. We can make a camera, and by means of reflectors or 

mirrors, form two or three focussing planes, each of which ap- 

parently receives the same amount of light-rays from that one 
lens, but when we try to form identical pictures, at the back in each 
separate focussing plane, then we find the same derogatory influence 
prevalent, as when wedge-prisms are employed. 

That the whole dividing proposition for the purpose claimed 
is a fallacy, is demonstrated very easily and conclusively, and I cannot 
understand that opticians and scientific instrument-makers, known 
all over the world should have staked their reputations on pro- 
positions touching their own trade, without verifying their state- 
ments, by a simple test in the camera. If even experts have lost 
their bearings in optical knowledge, appertaining to their own pro- 
fession, I must conclude that others only interested in such researches, 
must also be at a loss to understand, the effects and causes of 
splitting up a light-cone. I hope, therefore, to be kindly excused 
if I state my negations, and to do so my helpmates, photographs and 
drawings, will give the most convincing support. 


|: is very easy to divide a light-cone into two or three parts behind 





Fig. 11.—Sky screening. 


In an ordinary camera I introduced, not a transparent or re- 
flecting mirror, but simply a solid block, in such a manner, that the 
lens was half covered, up to the optical axis (see Fig. 11), then I 
photographed some printed matter from the Nineteenth Century 
(see Fig. 12), but so that the black line corresponded to the optical 
axis and the inserted block; and in the photograph it is seen that 
the word ‘“ Century” is fully and correctly reproduced, but the 


22 COLOUR PHOTOGRAPHY 


other half is shaded off, because not all light-rays go through the 
optical centre ; there are light-rays, which pass the periphery of the 
lens, as shown by the broken line arriving at “‘d” (Fig. 11). If now 


h Century 


ge 





Fig. 12. Sky Screening. 


we place a reflector or mirror in exchange for the block, is it to be 
believed, that the word “‘ Century ” would then wholly or partly be 
reflected in the other half and substituted for ‘* Nineteenth ” ? 
Anyhow, that is what was expected and asserted to be the case. 


i *mae 





Fig. 13.—Panorama-like continuation 


For those to whom the foregoing explanations are not yet 
sufficient, I add a drawing ‘‘ Panorama-like Continuation ” (Fig. 
13.) The two mirrors “ M1” and M 2” divide the sight into two 


EXCENTRIC PROJECTION 23 


parts, and it is immaterial, if the part-picture is reflected by the re- 
flector “‘ R” or not, it will remain a part-picture, and the two-focus 
pictures are therefore, each furnishing only half the picture, necessary 
to form one continuous whole picture, which latter could have been 
obtained more easily with one lens in one focussing plane. The 
exposure graduation, of the two part-pictures and three part-pictures 
is also given in the smaller illustrations in the same figure, to show 
conclusively that such pictures are not alike to, and will not, superpose. 

The pinnacle of ingenuity in ‘“‘ inventing ” an “ invention ”’ is, 
however, reached with the proposal, to form three separate pictures, 
by the displacement of the optical centre in the one lens, by means 





a DMNNMSSFEKK™bh Fo 


Fig. 14.—Peripheric projection. 


of three excentric stops. The illustration of this proposition “ Peri- 
pheric projection ” (Fig. 14) shows really more than the lens can 
transmit, but is what the inventor thought could be done, and if it 
had been possible, then, stereoscopic differences would have come to 
light, because the two blocks “a” and “c” are seen in a different 
aspect, as when photographed at equidistance from the lens centre. 
A lens has great likeness with the behaviour of wedge-prisms, 
which likeness we specially notice, when photographing an object 
with one lens, into which latter we have inserted an excentric opening; 
the distance “ a, b, c,”” when reproduced, is curtailed at the most re- 
fracted side of the light-cone, so that the two pictures “‘ F 1” and 
F 2” will never completely meet as shown in the graduated scale. 
This curtailment of the graduated scale depends, somewhat, on how 


24 COLOUR PHOTOGRAPHY 


far the artificial lens centres are placed away, from the actual or 
natural optical axis, but it is certain, that wherever the excentric 
stops are, they do not eliminate the foreshortening defect. The 
smaller triangular illustration shows in a general way, how the three 
pictures obtained in the three focussing-planes “‘ F 1,” “ F 2,” F3”’ 
fit together, and how far they superpose. 

I have an idea that three lenses placed close together, passing. 
as little stereoscopic differences as possible, would fulfil much 
better the requirements for a triple camera for the subtractive method 
of colour-photography. 

Similar misapplications in optics exist also in the spectacle 
trade. When you order bifocal glasses all tests are correctly made 
through the centre of the test lenses, but the manufacturer without 
any misgivings transposes the action into a peripheric one and if 
you see colour fringes, he stoutly disclaims any liability or the 
possibility of such a thing. 


DOUBLE REFLECTIONS 25 


Cra Er Re VILE. 


DOWUBEE REFLECTIONS 


refracted picture, but we have also to know what happens on 
the other side of the glass, used as reflector and filter—we have 
to know the crucial facts of the reflected light-cone also. 


{ N one-exposure cameras we have not only to account for the 


Cc 

eS ee Bl 
mean PINS EN ae ol a cater 
Fi a ibi Ly 
\ i : ' 












| 
| 
( 
( 
| 
| 
! 
\ 
1 
ye ; 
‘ 
4 






LLL CALLE LLL 


Fig. 15.—Ordinary reflection. 


If we follow, as shown in the drawing, “ ordinary reflection ” 
(Fig. 15) the rays “‘ L,” part of the same will be reflected by the first 
surface “‘ S 1” of the glass to a first focus “‘ F 1,” a second part of 
the same light-cone will pass and be refracted by the same surface 
“S11.” The refracted light-rays “‘ R ”’ will be deflected to the back 
or second reflecting surface “‘ S 2,” where the same partition of the 
light-rays is repeated, and the reflected rays “‘ r ” are again refracted 
on their return to the first surface “‘ S 1,” and eventually come to a 
second focus in “‘ F 2,” which latter is about half a glass-thickness 
inwards, or shorter than the main or first focus. 

The secondary light-action will however, pass over the inner 
focus plane, and on arriving at the exterior focus plane will show to 


26 COLOUR PHOTOGRAPHY 


some extent as a secondary picture, if exposure is made on a photo- 
graphic plate. This weaker or second picture, if slightly less sharp 
and displaced,must be elongated when it arrives on the focussing-plane 
of the first and direct reflected picture, contrary to the refracted and 
fully transmitted picture, which latter is partly narrowed down. 


The secondary reflections are also subject to what is called 
*“ spectral dispersions” and this latter would also influence the 
sharpness of the secondary picture. Granted that these rays are 
slightly out of focus and unable to form a very sharp picture, they 
would as ghost-pictures seriously interfere with the true picture 
formed in the main focus by the direct reflected and, therefore, 
predominant rays. 


We have means to suppress the secondary actions of these rays- 
We can make them non-actinic through absorption and by using 
photographic plates which see only one colour. 

In a one-exposure camera the best white optical glass covered 
as a rule on one side with a vehicle holding colouring matter is used 
for the reflector or mirror, and is often referred to as transparent, 







MUTT ETTETEMA ESTES. 


CLT TLLLL LLL 


Fig, 16.—Prism base up reflection. 


reflecting, transmitting, refracting filter or reflector. The vehicle 
is generally coated on the second surface, and if red would impart 
red on the secondary picture, and absorb the blue light-rays to a 
very great extent. 





DOUBLE REFLECTIONS a7, 


The interposition of a red light-filter, acting as reflector-filter, 
will affect in a similar way the transmitted light. It will absorb the 
blue rays, even in the prismatic dispersion which is introduced 
through the first surface. For the purpose of absorption of the blue 





Fig. 17.—Prism base down reflection. 


rays in the secondary reflection, a reflector coloured in the glass, is 
still better; such a reflector must, however, also be faced with a 
“coloured vehicle’ in such a manner as to fully correct the filter 
for the transmitted rays. 

Silvering, platinizing, varnishing, etc., of the first or main 
reflecting surface has been advised to augment the amount of re- 
flected light, and in order to eliminate the double reflection, but if 
applied, only surfaces are introduced, which are subject to tarnishing 
and gradual loss of reflecting power, and this on the very surface, 
where stability of reflection is the predominant desideratum in such 
a reflecting system. . 

It has been suggested by Ives to use wedge-shaped prisms to 
disperse the double-reflection. I have made two drawings— 
““ Prism base up reflection’ (Fig. 16) and “‘ Prism base down re- 
flection ’ (Fig. 17) to show that this very scientific suggestion simply 
displaces the secondary focussing plane and that in certain parts 
Boumeroc of 1 and ~“F 2” touch each other, giving there a 
much better impression of the secondary picture than parallel plate 
could ever give. 


28 COLOUR PHOTOGRAPHY 


If, however, we consider that wedge-prisms, of much lower 
degrees as shown in the drawings, can possibly be used, then the 
introduction of such prisms seems of doubtful utility, and they be- 
come positively harmful to the transmitted pictures, which is ascer- 
tained when the consequences of refraction have to be drawn for 
that purpose. 

When we come to camera systems with several internal re- 
flectors, we must consider the consequences and have some idea as 
to what internal reflections will do, say only between a few parallel 
surfaces of glass. To come to a sufficient understanding, I can 
suggest the following :—Sitting in a tramcar at evening time, you 
can easily admire yourself or the lady at the furthest corner, or you 
can see what is going on or passing in the street, at the back of you, 
or in front of you, and all this whilst sitting perfectly still and losing 
yourself in the kaleidoscopic reflection. Further, imagine what the 
addition of some more reflecting surfaces may bring about, and apply 
the conclusions to the reflector systems of cameras, and you will 
understand much better than I can tell you, why reflector One- 
Exposure Cameras, with more mirrors than one, are only theoretical 
illusions, and scientific experiments applied ad absurdum. 





INCORRECT REFLECTIONS 29 


SARE R Lx 


INCORRECT REFLECTIONS 


reflected from a plain reflecting surface would, on arriving 

on a focussing plane, give a correct representation of the 
respective projected image of which the lens is the medium and the 
light-cone the optical field. The interposition of a reflector, con- 
sisting of a glass from one-tenth to one-third of an inch, does not 
really affect the transmission very much; if a smaller stop is used 
the introduced unsharpness is not noticeable, and only a trained eye 
would see the small displacement caused by a glass when placed at 
an angle of 40 or 50 degrees into the light-cone. The refraction 
defect imparted is so very small and by some experts is even now 
declared to be an illusion and non-existing. 

A glass placed as suggested above and as used 1n a one-exposure 
camera plays, however, undeniable havoc with the reflection if in 
the slightest way out of its proper position. It alters the focussing 
direction. 

In my drawing “Incorrect reflections” (Fig. 18) the light- 
cone coming from the optical centre ““O”’ is reflected by the re- 
flector “‘R 1” inclined at 45 degrees and arrives at the focussing- 
agent o. | Lhe central: ray of this cone “ C 1” is reflected at 
the pivot ‘‘ P ” and arrives at ‘‘ d”’ when the two half-cones “ bd” 
and “‘ df”? are shown to be of equal or balanced width— 4o points 
each side—therefore together 80 points. 

As an alternative, if we now give the reflector an inclination, 
of say 40 degrees, ‘‘ R 2,” then the central ray ‘‘ C 2 ” also passing 
over “‘ P” will, on arriving at the focussing-plane “‘ F 1” be dis- 
placed to ‘“‘c.”” When we find the “ a-c”’ half-cone 44 points wide 
and the other half-cone “ c-e”’ only 40 points wide, the full cone 
covering therefore 84 points of the original focus plane “ F 1,” is 
therefore not balanced and is occupying more space. This irregu- 
larity would show itself in a picture as unsharpness, being out 
of focus at both ends, similar to a badly adjusted swingback, a thing, 


| i to now we have taken it for granted, that whatever was 


30 COLOUR PHOTOGRAPHY 


by-the-by, that cannot be used in a camera with more than one 
picture-plane. 

On the other hand, if the reflector is inclined at 50 degrees 
““R 3,” exactly the same irregularity takes place, but the larger 






LITT 72 


CLLILITLLTTELTT) 


O 





Fig. 18.—Incorrect reflections. — 


half-cone is now towards the “‘ g ” and not towards “a” as in the 
second case. 

I have to point out these irregularities, because the camera being 
once constructed, cannot be altered, only the reflector can be moved 
and in doing so, one may easily under or overdo the packing on one 
side more than the other. If, however, the focussing planes for 
F 2 or F 3 can be adjusted at right angles, to the central ray “‘ C2” 
or “‘ C 3” respectively, then the two sides of the light-cone will be 
balanced as in the case of. focussing-plane “‘ F I ” in connection 
with the ray “ C 1,” but as I said, if the focussing planes are once 
fixed then no such alterations are possible to the person not initiated. 

An American inventor has filed several patents in which he 
introduced a plain transparent reflector inclined at 45° to the central 
ray. I have also inclined such a glass in my camera and upon 
trying to find the focus I came to the conclusion that a real photo- 
graph of the observed phenomenon would speak much better of the 





INCORRECT REFLECTIONS 31 


value of the invention than anything I could say. It had evidently 
never been tried before the patents were obtained. The two photo- 
graphs (Fig. 19) were taken simultaneously in a one-exposure camera 





Fig. 19. 
Refracted picture above; Reflected picture below 


32 COLOUR PHOTOGRAPHY 


having a plain, not coloured, reflector. One view is by refraction 
and the other by “‘ double ”’ reflection. 

If, on the other hand, the reflector filter is of yellow (or green) 
glass coloured in the mass, yellow would be reflected by both sur- 
faces and if such a reflection impinged on a yellow sensitive or 
panchromatic plate, similar double exposure would result. 

It seems to me worth while to know all these little intricacies 
the one-exposure camera work is heir to. We are all so liable to 
take many things as obvious, and if you try to disprove an “ obvious 
thing ” you are often called a fool. 





CURVED SURFACES 33 


CUS DAM OTT BIN Oe 


BukVEDS SURFAGES 


VES in his patent 2305/95 inserted plates at 20 to 25 degrees 
[ inctnstion, and describes them as light filters, but for what 

purpose they were so inclined is not disclosed, perhaps to over- 
come internal reflections. (Twelve years afterwards he based a 
claim on this position stating the same to be a described compen- 
sation for the refraction defects.) But only four years later he filed 
a compensation patent in the States. 





Fig. 20.—Reflection and _ refraction. 
Curved parallel surfaces. 


On the fourth day of April, 1899, letters patent numbered 
622480 was granted to Ives in the United States, describing and 
claiming a.method of distorting the reflected picture also by the 
application of local pressure to the reflecting surface of the trans- 
parent mirror by means of springs or other pressure devices. 

The English patent 3872/13 is for “ other pressure device ” 
granted to the Dover Street Studios, no application being made for 
same in the States. 

My drawing ‘ curved parallel surfaces”? (Fig. 20) shows in 
exaggeration the effect of pressure applied to the reflecting surface 


34 COLOUR PHOTOGRAPHY 


and it is evident that more distortion pure and simple is thereby in- 
troduced, therefore no correct compensation, for the simple reason 
that no pressure device could ensure an equally balanced pressure 
all over the reflector. 

The drawing shows that the reflected picture in the focus, when 
the hollow or bent side is facing the lens, is narrowed down from 
80 mm. to 65 mm. as compared with the original focus, and is also 
curved in at the focus plane, and at the same time the refracted 
picture is widened out, from 80 mm. to 95 mm. (3} to 3$ ins.) with 
the curved focus in the opposite direction. This curvature can 
also be placed in the hollow or bent side away from the lens, when 
the reflected picturewould be larger,and the refracted picture smaller, 
and the curvature of the picture would also be reversed. If this 
curvature is imparted cylindrically, the picture would be deformed 
in that direction only, and if the curvature forms parts of a globe, 
then the image would be affected that way. 

I think I am right when saying that if such curved reflectors 
are inserted into cameras, and the focus is adjusted for one lens and 
one distance, then a fresh adjustment is required if employed for a 
different distance, or if another lens is inserted having a different 
focus. Therefore only cameras having a fixed focus could be em- 
ployed if such pressure device is to be applied with success to the 
reflector. 

The above are the only two known patents claiming the cor- 
rection of the reflected picture only, so it is still open for an inventor 
to patent the correction by way of refraction-distortion, but before 
losing his money in a patent speculation, I advise him to have a good 
look into a mirroscope having a cylindrical mirror, or to admire 
himself in a silvered globe, optical appliances which have been 
patented to obtain distorted photographs as claimed in Patent 
22825/08, by Hamburger and Costen. 

The circular distortion with globe-like surface can also be 
obtained without any pressure device, if a thin glass reflector is 
covered with a contracting vehicle, such as gelatine, when dry. 
This substance being hygroscopic, has to be protected, but even 
when protected could as little be depended on as the mechanical 
distortion device named above, and this idea is not patented yet, 
nor are the following ones. A slanting glass reflector, if thin enough, 
will sink in towards the centre if fixed in a frame, similar to a blanket 
hung up at the different corners, or the same glass reflector will 


a 


— 


CURVED SURFACES 35 


bend cylindrically if only fixed on one side, so that the main body. 
stands out sideways in the camera, and we must not be surprised 
to hear one morning that a collodion film stretched over a frame 
has been suggested as a reflector. 

In the above I have not touched on the atmospheric influences, 
the expansion by warmer, and the contraction by colder surround- 
ings, and I think there is no doubt that such influences do not make 
for stability of the reflecting surfaces in any pressed or coated re- 
flector-filters. 

The tension exerted by a gelatine surface is noticeable in a 12 
by 10 inch plate, having a thickness of one-eighth of an inch. 


36 COLOUR PHOTOGRAPHY 


CHOAP PERG OE 


SOME COMPENSATIONS 


ONTINUING the enumeration of the possible compensa- 

tions in one-exposure cameras in which the light-cone is 

refracted, I now have to deal with Ives’ device of compen- 

sation with right angle prisms, a device that once had been recom- 
mended for viewing stereoscopic pictures. 

The illustration (Fig. 21) shows, that the geometrical condition 

forming two focussing planes of same size with paired and equal 





Fig. 21.—Compensation with right-angle prisms. 


refraction is really the accomplished fact; we have to ascertain if 
the scientific proposition is also fulfilled. Seeming facts are often 
negatived by further investigations; the paper is very tolerant and 
the patent office is always glad to take the money, even if the inventor 
has not verified his facts. 

A prism combination as here proposed will not form a picture 
in “ BF” at the back, but only in ~ TP thetope onesie ee 
hand, if the two prisms are cemented together, then no internal 
reflection to “TP” takes place, the two prisms simply forming 
a cube in which the picture is only visible at ‘““ BF ” and that very 
likely slightly displaced, the Canada balsam being of a slightly 
different density. To form a picture in each proposed focussing 
plane we must have one of the surfaces silvered, where the prisms 
join each other at “P.” The silvering has to be balanced in such 
a manner as to be partly transparent and partly opaque, and when 
that is attained it requires a conjuring trick to cement the two. parts 


———— a 


SOME COMPENSATIONS 37 


together with Canada balsam, without injuring the silvered deposit. 
When all this is accomplished, it will be found that the refraction 
defect has not been completely eliminated, and that a slight dis- 
placement of the back-picture is still present, therefore, giving an 
incorrect picture. Even if the compensation worked completely 
and correctly, what about the loss of light and the cost? The latter 
would be prohibitive even for a quarter-plate camera. The whole 
proposition resolves itself into a scientific plaything of no value 
whatever. The inventor gained thereby, no doubt, the scientific 
halo of being a very clever man. 





Fig. 22.—Wedge Prism Compensator. 


The investigation of wedge prism compensation is our next 
proposal (Fig. 22). We have seen in a former article, that in the 
ordinary way, when using parallel plate as a reflector filter, the 
difference of the refractions at R 1, and R* 2, is the cause of the 
pressing together of the light cone forming the back picture, and it 
was suggested, to make the refraction at R 2 of the same length as 
at Ri. If we adopt that proposition, the two surfaces of the re- 
flector will no more be parallel but convergent and the reflector 
will have the appearance of a wedge, 7.e., narrow-angled prism. 
I should think such wedge prisms in larger size would be expensive 
and the complete problem would only be solved for a fixed focus 
camera. 

For each lens and for each different focus distance another 
wedge prism has to be exchanged, calculated for that very focus 
required. Moreover, the refractive displacement of the picture at 
the focussing plane has also to be investigated. There are altogether 
quite enough disabilities, to justify us in dismissing the wedge prism 
compensation, as of no use in one-exposure cameras. 

The wedge prism has, however, also been advocated by Ives for 
the specific purpose of dispersing double reflections, which was 
dealt with in Chapter VIII. 


38 ' COLOUR PHOTOGRAPHY 


A curious, but scientifically correct self-compensating action 
(Fig. 23) has been patented by O. Pfenninger. Fig. 17 of Specifi- 
cation 26609/1910, of which I give an illustration, embodies the 
invention. | 





Fig. 23.—Colour camera with self-compensating reflector. English specification 26669/1°. 


The lettering r-s-t-u shows how the reflector in a Bennetto 
Camera is placed. The present way of placing the reflector is 
shown, and marked v-e-f-u, which position places the refracted 
picture over the diagonal a-c. The foreshortening is therefore 
equal on the sides joining each other a-b and a-d, and the whole 
refractive action is only by accumulative refraction, described in 
Chapter V. 

The reflection is also thrown sideways and necessitates the 
peculiar shape of the camera box. It is said that this patent has 
been partly acquired for U.S.A., and the patent is accepted by the 
United States Patent Office without opposition. 

It is very interesting to know that this is the camera which 
Dover Street Studios used in I9I11I-13 in taking successfully by 
instantaneous exposures three correct colour negative records, 
size 12 by 10, the illumination being a magnesium flash. 

For the Polychromide printing process used in the same studios, 
carbon pigments were at first used, with an alternative for the yellow, 
for which a bromide print was toned (converted into) a yellow print 
with mercuric iodide. 





BENNETTO’S SYSTEM AND COMPENSATION 39 


GEAR IER xl): 


BENNETTO’S SYSTEM AND 
COMPENSATION 


camera system, English patent 28920/97 (Fig. 24). The 

system is on the simplest lines possible, having only one 
reflector. It is, therefore, an absolutely independent invention, free 
of any anticipations and cannot be ranged with the two or three 
reflector systems. Since it has been proved that this is the only system 
with a future, other inventors have claimed the same as being included 
in patent claims of the older systems, but I have looked up all the 
different patent specifications relating thereon, and they all speak 
of “‘ reflectors.”” Now in two Bennetto cameras there would really 
be two reflectors, but only one reflector in each separate camera. 


‘ LREADY several references have been made to Bennetto’s 





Fig. 24.—]. W. Bennetto’s Patent 28920/97. 


In Bennetto’s system, one light-filter ““P”’ is introduced as a 
reflector filter, and is inserted at an angle of 45 degrees into a box, in 
such a manner, that the light cone is reflected to the top “‘ TP,” to 
form a focussing plane. The reflector filter is however transparent, 
and some part of the same light cone, is passing through the same 
reflector filter to the back focussing plane “ BP,” this back- 
picture being foreshortened as already explained. (Page 15). 

Bennetto’s original system is not well adapted for the sub- 
tractive method, because a casing, to eliminate the extraneous rays, 


40 COLOUR PHOTOGRAPHY 


is not provided. We have, therefore, to use an “‘improved one- 
reflector camera ”’ system (Fig. 25) for taking negatives. These two 
systems. can be used for the additive method, but even with such 





Fig. 25.—Improved One-Reflector Camera. 


an improved system we do not obtain pictures of the same size 
only a picture that is clearly transmitted and a picture that is clearly 
reflected, with the help of block “‘ BE.” 

The ‘“‘ Compensated Bennetto Camera,’ (Fig. 26) English 
Patent 25907/06, by O. Pfenninger, shows us that when inserting a 
compensation plate, in preference, to the refracted light cone, the 
inventor obtains two equal pictures, because he inserts a compensa- 
tion plate in the refracted light cone, after the reflector filter, in such 
a manner, as to obtain pictures free of any distortion. 





Fig. 26. Compensated Bennetto 25907/06. 


If a-b-c-d is the upwards inclined reflector filter, then e-f-g-h 
is the sidewards inclined compensation plate, inserted so that the 
picture, already compressed and refracted in one direction, is a 





BENNETTO’S SYSTEM AND COMPENSATION 4I 


second time compressed and refracted, but in the other or cross 
direction, the inclination of the reflector and the compensation plate 
being the same, and the two plates of the same thickness. This 
compensated system furnishes two picture planes, of which the 
back picture is narrowed down horizontally, as well as vertically, 
to the same amount, but both picture planes are of exactly the same 
form, and to bring them to exactly the same size the back focussing 
plane has to be adjusted by being placed further away. The dis- 
tance of displacement is about + of the thickness of one of the plates. 

This displacement of focus is necessary to obtain a picture as 
sharp as the top-picture, because the refraction displaces not only the 
focus as to size of picture, but also as to sharpness. 

When the camera is worked, a pack of two plates, film to film, 
is taken in one focussing plane, and one plate in the other focussing 
plane. The filter arrangement and the respective focussing planes 
naturally depend on this, and are a matter of pre-arrangement. 

From the negatives obtained with the improved Bennetto 
camera, it would, with the aid of slanting and upright parallel plates 
in the copying apparatus, be possible to make corrected glass posi- 
tives, but it is preferable to take the negatives in the first instance 
with a fully compensated camera. 


42 COLOUR PHOTOGRAPHY 


CHAP TER. XT 


COMPARATIVES AND ANOMALISM_ IN 
REFLECTOR: CAMERSS 


especially as applied to colour-photography, seems desirable 
and I hope may be instructive. 

In a general way we are always informed of all the “‘ expected 
merits’ of an invention, but when the expectations have broken 
down, nothing further is heard of the same, and this is only too often 
a sign that the inventor lost himself in “ theoretical suggestions ”’ 
before applying the “ practical test.” The press, always eager for 
*“ copy,” publishes the information or news without regard to cor- 
rectness, originality, possibility, etc. My specific intention is to 
have a peep behind the curtain of lost expectations in respect of 
reflector cameras. 

So far back as the sixties it was recommended to place a solid or 
translucent shield at a certain distance in front of the lens when 
photographing a landscape, so as to shade off the sky. With such a 
medium it is possible to shade off the plate from the centre so as to be 
transparent on one side. 

In the studio the same idea is now used. A vignette, or a part 
of a vignette, cut out of translucent or opaque material is placed 
before or behind the lens, ata certain distance to obtain the white or 
dark vignetted pictures now in vogue. The latter were first shown 
at the International Exhibition, Paris, 1878, by a court photographer 
from Petrograd, and awarded the Grand Prix. 

Two opaque flaps (not mirrors) in connection with one lens, are 
placed so that one exposure of a person could be made on the left 
side of a plate and a separate second exposure of the same person 
on the right side of the same plate, showing afterwards as “ self 
shaking hands with self”; this is a similar application of the sky- 
screen idea. 


‘ CRITICISM on reflector cameras in an objective way, 


Since 1899 a multiple of this sky screen in one way or another 


forms the corner stone of some inventions for reflector cameras. 


Oe a ee a oa 


COMPARATIVES AND ANOMALISM IN REFLECTOR CAMERAS 43 


The first intimation of this extraordinary invention came from the 
United States of America. In this invention the halving of the 
light cone in front or at the back of a lens (as shown above), is not 
done by two flaps, giving two “ different pictures ” by two exposures, 
but by means of mirrors or prisms, and duplicates “‘ all alike ” of 
one object at one exposure are now said to be obtainable. There 
are several different inventions on the same line of thought standing 
to the credit of that American inventor. Now I grant that by these 
means it is possible to obtain several illuminated fields or a “ different”’ 
picture on each field at one exposure, but the same amount of picture 
of the “‘ same ” subject in all fields.as required for a one-exposure 
colour camera is “ unattainable,” at least on this side of ‘“‘ the pond.” 
Perhaps the light and optical conditions are different on the other 
side, and the light rays travel round corners, not through the centre 
of a lens. 

The first whisper of this new colour camera encouraged other 
inventors in the old countries, not suspecting tall stories, to 
enter this sky screen competition, which became keen, and several 
dozen patents vouch, not for the acuteness of these inventors, but 
for the money paid to the State. These discoveries all belong to the 
paper inventions. There is no doubt that they are “ real inventions ”’ 
of over-smart people, because the facts of real possibility were never 
verified, and I doubt if any of these suggested cameras were even 
constructed, because if they had been, the fallacy would have been 
only too apparent. As it is a certain halo as a compensation is still 
attached to these pioneers of failures. 

The principle of Bennetto’s system, the one reflector camera, 
has lately come to be recognised as the nucleus for a one-exposure 
camera. It is now known that the light reflected in such a system 
is about one-ninth part of the light cone; the absorption of the 
transmitted light through the orange-red filter 1s about six-ninths, 
leaving a two-ninths part of light to act in the direct light cone. 
To meet this difference between the reflected and transmitted light 
action, it has been recommended to silver or platinize the reflector. 
If the surface of the glass is too strongly metalled, it will be too opaque, 
preventing the passage of light, and if the metal surface is so thin and 
transparent as to balance the transmitted and reflected light action, 
then the metal coating has no resistance to withstand the polishing 
pad, and if varnished will not present a better reflecting surface than 
the ordinary polished glass. 


44 COLOUR PHOTOGRAPHY 


Cross-cutting the metal surface so that the surface resembles 
a half-tone screen introduces defects similar to the following in- 
genious device, which is, a part-perforated reflector-filter, and it 
looks perfect on paper, but if dissected, it simply amounts to the 
placing of several (say 10 to 20) sky screens or “‘ vignettes Russe” 
to the square inch. The glass in the perforated, and therefore 
transparent, parts eliminates the refraction defect to perfection, but 
what about the action of the perforated screen on the photographic 
plate ? 

Let me apply the conditions of a ruled screen (to which the 
perforated screen is akin) of the half-tone process worker to a quarter 
plate one reflector camera actually in use. The data is as follows : 
Camera extension 18 cm., and a variant of 25 cm., focal length. 
The light cone passes through the reflector filter, which is inclined 
at 45° when the extreme light rays would give about 5 cm. and 12 
cm. screen distance. The screen opening, that is here the perfora- 
tions, we take for one calculation to be 1 cm. and for an alternative 
4 cm.; in which case the stop required for a half-tone dot is 
found as follows :—The calculations being made in millimetres. 


Screen Camera Screen Size 
opening. extension Sum. distance. ' of stop. 
10 x 180 = 1800: 50 = 36 mm. 

10 x 180 _ 1800 "22 atae = L5iae. 

5 x 180 = goo : 50 == IS 

5 x 180 eS 900° aaeei2o oe 7 Se 

IO x 250 = 2 500M 50 = 50. 4; 

10 x 250 = 2500 = wier20 om Zl os 

5 x 250 “= 12501 50 = 25 Cass 

5 x 250 a 1250) [reo = IOs s; 


A 25 cm. or I inch stop is as seen a good size stop for general 
use or under above conditions for half-tone dots, and a smaller stop 
would allow a still greater screen distance, or would accentuate the 
screen pattern on the plate still better. If the perforations in the 
reflector-filter are larger than the stop, then no perfect dots would 
be formed by the light, but some pattern of the screen would still 
be imparted. It is noticed that at one end of the plate the condi- 
tions for a half-tone dot are perfect, the slanting perforated screen 
would naturally impart a certain degradation and the plate would 


_ 


COMPARATIVES AND ANOMALISM IN REFLECTOR CAMERA 45 


present a certain irregularly spotted pattern, but never a uniform 
picture. 

What about the reflected image ? Well, the same will represent 
exactly the reverse appearance to the transmitted image and also in 
exact proportions to the missing or cut-out reflecting surface. 

If you look in your own looking-glass having a hole in it, or an 
Opaque paper patch on it, it will prevent you seeing yourself to the 
extent of the missing reflection, and if you hold an opaque patch 
between you and the mirror (like a sky screen) it will by no means 
improve the reflected image—it is all so obvious—and yet, when 
applied to a photographic camera, specifically for colours, Munch- 
hausen or Don Quixote rushes into print, feeds the Patent Office 
with cash, defies the optical laws, boasts of special scientific know- 
ledge, and thoroughly wastes his energy. 


46 COLOUR PHOTOGRAPHY 


CHAPTER XIV. 


ADDITIVE AND SUBTRACTIVE LIGHT 
PROJECTION. 


manifested itself to take three negative colour records for the 

subtractive method ; an easy photographic printing method does 
not exist even now; the carbon printing is still the best, but the 
photo-mechanical process by three-colour blocks has made impor- 
tant progress, and it is for this means that three colour negatives 
are in demand. | 

I think it advisable, therefore, to illustrate the camera required 
for the additive as well as for the subtractive method of colour 
photography, and indicate the requirements and differences between 
the Du Hauron-Ives Camera and the Cros-Ives Camera as applied 
to the one reflector or Bennetto’s System. 


|: is only since the beginning of this century that a real desire 


ayelq Aug 





Dry Plate 
Fig 27.—Light Action in One-Exposure Camera. 


b 


The illustration (Fig. 27) “‘ light action in one-exposure camera’ 
shows how the lens distributes the light rays in a camera. A block 
** B C,” has to be inserted to cut off some light rays to protect the 
horizontal photographic plate from direct exposure to the rays, 
because the same should receive the light from the mirror “‘ P ” 
only, even then the peripheric action of the lens may pass some ex- 
traneous light as indicated by the tangent “E.” If, however, the 
block ““B C” is made higher, then we are likely to cut off some rays 


ADDITIVE AND SUBTRACTIVE LIGHT PROJECTION 47 


which are necessary to complete the back picture. At the meeting 
points of the two focussing planes a cut out could be inserted, and 
must be inserted, if the camera should be used for taking negatives, 
that is, to fit the camera for the subtractive method. In all Ives’ 
patents the latter requirement is never alluded to, nor have I any re- 
collection of a block “‘ B C,”’ being recommended by Ives in any 
of his two reflector instruments. 





Fig. 28.—Light action in Chromoscope. 


The drawing (Fig. 28) “‘ Light action in a Chromoscope ”’ 
shows that the light rays enter through the glass positives only, and 
an extraneous light ray “‘ E ” has no disturbing effect on the viewing 
eye at the ocular, and this is the condition of all the Chromoscopes 
standing to the name of Ives. 

After seven years of hard work inventing viewing instruments 
for the additive method of colour photography, Fred. E. Ives finds 





Fig. 29.—Photo-chromoscope. F. E. Ives, U.S. patent 635,253, 17 Oct., 1899. 


that a refraction compensation is required. He has no great opinion 
of it either, because he files one in U.S.A. only, 635253 on 7th 
October, 1899. I can trace no English equivalent. The annexed 
drawing (Fig. 29) shows that only the reflected picture is narrowed 


48 COLOUR PHOTOGRAPHY 


down to bring the same to the size of the refracted picture. The 
double compensation ‘‘ DC,” and the single compensation “ SC,” can 
also be inserted at right angles instead of parallel to the mirrors R 1 
and R 2, without altering the compensating effect. This, however, 
is not claimed in the patent specification. 

The picture in F 3 is twice refracted and twice foreshortened 
by the reflector filters R 1 and R 2; the picture in F 1 is fore- 
shortened to the same amount by an inserted plain parallel plate in 
thickness to the sum of the two reflector filters ; the middle picture 
in F 2 is once refracted and partly compensated. The compensa- 
tion is claimed for a three-focus instrument, all pictures being fore- 
shortened. 

The tangent “ T ”’ shows that the last focussing plane is exposed 
to extraneous light, if such an instrument is used as a photographic 
camera; the apparatus is therefore a viewing instrument pure and 
simple. Other variations of the apparatus given in the patent 
specification are more condensed and, therefore, subject to more 
extraneous light actions in the focussing planes. 

The patent specification says, as follows :—‘‘ The object of my 
present invention being to introduce in a reflected image or images 
a distortion corresponding to that produced in a transmitted image.” 
Therefore a compensation introduced which does not distort the 
pictures would be an improvement not claimed by Ives. With 
such an improvement we deal in another article. 


COLOUR ENIGMAS 49 


SPER XV, 


COLOUR ENIGMAS 


printing in colour, to which has to be added all the im- 

purities incorporated with the colours, the adding of 
varnishes and other vehicles to hold the more or less transparent 
pigments of colours, then we shall find the most brilliant blue, 
yellow or pink will suffer, when the colours are superposed, and that 
these conditions are the principal reasons, why the top colour, from 
the three superposed in a colour print, will always impart a pre- 
dominant hue. 

The difference between theoretically demanded pigment colours 
and those in existence, represent metaphorically speaking, an aspect, 
as, if you superpose in the first case pure transparent glass on a pic- 
ture, and in the second case, if you superpose more or less finely 
grounded glass, and if this ground glass were ever so faintly coloured, 
it would not only degrade the colours in your pictures, but also 
impart a hue. 

A similar aspect exists with reference to transparencies. You 
may look with satisfaction at a transparency made at home, and find 
it quite right, when viewing the same by daylight ; then when you 
send the same to an exhibition, the show will be arranged with arti- 
ficial light of one sort or another, thrown on a reflecting surface, which 
consists of grey-white, creamy-white, bluish-white or other white 
paper, and your transparency, which you thought perfect, will show 
in this transmitted and reflected light a wishy-washy nondescript, 
degraded in colours, with a predominant hue of some sort. 

I wish to point this out, because some experts, who judge your 
work, like to show off, and play on the transparent glass, “ variety, or 
daylight,” well knowing that it is impossible to attain the object of 
faultless colour mixture by superposition of the ground-glass variety, 
especially so if the necessary materials are not yet obtainable com- 
mercially in any acceptably pure conditions. 


WW visi we come to look up the possibilities of photographic 


50 COLOUR PHOTOGRAPHY 


When you have come to this understanding of degradations of 
colours, you will agree with me, that we should not speak of photo- 
graphy in natural colours, but only of photography in colours, 
especially so in reference to prints and less so to transparency. The 
theoretical investigator tells us that a pure blue, a pure yellow and 
a pure red will form all colour combinations, and that is why we also 
say “‘ Photography in three colours” or speak about a three-colour 
print, but, by-the-by, please do not inquire what a pure colour is, 
the experts are themselves not yet clear on the point, and very likely 
never will be, yet these colours are to be found somewhere between 
‘““B” and “ H ” in the spectrum, having a wave length of 700 to 400 
billion ether undulations per second. This statement is made only 
on hearsay—I never followed such giddy movements. 

One expert says pink colours are missing in the spectrum, 
another has his doubts about the yellow, but they all seem to have 
different shades of “‘ blues.”” The spectrum colours are formed by 
prism dispersion, and it is a mutable point, whether the prism itself 
does not deteriorate the spectrum colours, and if a “ grating ” is 
not more suitable. 


For us ordinary mortals, who have the inclination to apply 
everything to handy and practical use, there is no other help than 
to employ such colours as we can feel, and use them as pigments or 
as stains of vehicles, because I am positively assured, also on expert 
opinion, that it would, really be impossible to mix, these phantom 
colours of the spectrum, with any vehicle and so use them for printing. 


I have worked the carbon pigment printing process, which to- 
day is the coarsest ground-glass variety of colour printing on the 
market, but it is the only process which will give a few necessary 
prints to satisfy the man of smaller means, who is imbued with the 
colour-photographic hobby, and it enables him to make some prints 
to decorate his home with, as proof of his patience, endurance and 


will-power to overcome obstacles. But the process does not 


empower him to exploit the same commercially. 


The subtractive method is at all events something which adds 
a new power to the application of colour in art and colour printing ; 
further, if even all the applications are not natural in colours, we 
shall and do arrive at making artistic pictures and pleasing com- 
binations in colours, and we do arrive at the point of relieving the 
monotony of mono-colour prints. 


COLOUR ENIGMAS SI 


Allow me also to ask you not to set up chromo-lithographic 
productions, in which seldom less than twelve litho colour plates are 
used, as standard or minimum demand, in comparison with colour 
productions, in which only three colours are employed. There is 
no doubt that some of the early photochrome pictures show up 
the colours, showing something of—imagination, and some of the 
colouring is added in such a way as to give every advantage to the 
highest pitch of impressionism. We shall never be able to do such 
things with only three colours; it is absurd on the face of it to 
demand such exaggerations when limited to three impressions of 
colours only. 


§2 COLOUR PHOTOGRAPHY 


CHAP TER XVit 


ADDITIVE versus SUBTRACTIVE 


tive method,” the dividing and assembling of light rays, and 

the “‘ subtractive method,” by which pigmentary or dye colours 
are used in forming prints in colours. The scientific teacher has 
given a special nomenclature to his pet, which in this respect has 
always been the additive method of colour photography, and so it 
comes, that the subtractive method has come in for step-fatherly 
treatment. Primary colours is one of them, the easiest way would 
have been to speak about additive or theoretical primaries and, sub- 
tractive or printers’ primaries. The latter were described as 
primaries by the painters long before the spectroscope showed the 
possibility, that white light could be separated into colour rays. 
But no, that would have been too direct. The painter and printer 
use blue-green, yellow and pink, impossible for them to find a mix- 
ture of other colours to produce these three colours for him; you 
think then they are their primary colours. Oh! nothing of the sort, 
it 1s scientifically proved that blue-green is formed by all the spectrum 
colours minus orange-red, yellow minus blue-violet, and pink by 
minus green; the two colours always complement each other to 
form white together by projection, and it seems that the worker 
with “ solid ”’ colours sees the blue, yellow and pink only by “ re- 
flected ” light waves. 

The additive method of colour photography is the one which in 
its principles is the fulfilment of the scientific theories and explana- 
tions of light and colour. The text-books refer generally to it, 
when they give us their interpretation of primary colours, which 
seem to be violet, green and orange-red. These colours are best 
known in their application in the additive working instrument 
*““ Chromoscope,” and in the semi-additive colour-plate “ Auto- 
chrom,” and so it comes, that the modern additive worker feels in- 
clined, and even proclaims himself fully justified, to dictate his 
additive experiments on the worker with the subtractive method. 


“Tie principal divisions of colour-photography are the “ addi- 


ADDITIVE versus SUBTRACTIVE 53 


In the additive method you add the colours, not in matter, 
but in light rays, to form white, and the experience shows, that the 
filters necessary to obtain the negative colour-records are, as already 
indicated and specified about twenty years before Ives by Ducos du 
Hauron and Cros, violet (pink and blue), green (blue and yellow) 
and scarlet (pink and yellow) and not as generally described as blue, 
green and red, Ducos du Hauron having obtained his knowledge 
of the light conditions from the earlier works of Maxwell and others. 

From the negatives obtained through the above filters, the 
positives are produced in black and white in the ordinary way, and 
these positives are in conjunction with the same light filters re- 
united by projection, and therefore only light rays participate to 
form the result. The positive made by means of the scarlet filter 
negative record is projected with a scarlet filter, etc. 

If now we turn to the subtractive method, we use practically the 
same filters when using panchromatic plates, as for the additive 
method, to obtain the negative colour-records ; but the printing by 
colour material is different. If we add colour matter to colour 
matter, black will ultimately be produced. The negative obtained 
through the scarlet filter, also called the orange-red filter, and, if 
badly described, as the red filter, has to be printed in blue (note the 
difference from the additive method). The best blue is the shade 
“cobalt blue.”” The negative obtained through the violet filter is 
printed in yellow. It must bea yellow that, when mixed with the 
blue, gives a clear green like filter green, or if the yellow is mixed 
with the pink a clear scarlet is produced like the orange-red of the 
filter. The negative obtained through the green filter is printed in 
red; that is what we aretold. The red, however, is a pink, magenta, 
crimson, carmine; if this pink is mixed with the yellow the com- 
bination should be the same as filter scarlet and if this pink is mixed 
with the cobalt blue the combination should be the same as the 
violet of the filter. 

Some experts declare the filter-colours are blue, green and 
red, and say the negative must be printed with blue, yellow and 
red. That poor red colour! Anything dark-orange, scarlet, pink, 
rose-lilac, is called red. It is a marvellously accurate colour descrip- 
tion and is even employed by some people who fight over one 
millionth part of spectrum lines, where this or that colour begins 
or ends in the spectrum. 


54 COLOUR PHOTOGRAPHY 


CHAPTER 2 yy Ha 


FILTER ARRANGEMENT 


plate, I have spoken of the reflector filter being orange-red, 

the back-surface of such plate being surfaced with a medium 
holding the filter colours. This is a very good filter arrangement, 
and was specially so at the time when rapid red sensitizers were not 
known ; it is based on Bennetto’s ideas as given in his patent specifi- 
cations. This system has, however, a slight drawback, and that is, 
it allows internal reflections which, when bright subjects are photo- 
graphed, produce the picture in the top focussing plane with 
double lines, which are specially noticeable if fully or over-exposed. 

On the same photographic plate one picture is formed by the 
direct reflection, and a second picture (if weaker) has its origin in 
the double refracted reflection. This latter can be killed actinically 
by using a reflector coloured yellow in the glass mass. 

This yellow reflector can be surfaced with an orange-red vehicle 
or a separate coloured compensation (compensation in respect of 
the filter colour only) plate can be inserted, either parallel with the 
reflector, or the refraction compensator can hold the filter com- 
pensation, or this colour compensation plate can be inserted into 
the dark slide. In this latter case it would, without destroying the 
effectiveness of the filters, enable the operator to see the picture 
much better when focussing. This latter arrangement amounts to 
one fixed and one removable filter. 

The advantage of a picture cone passing through a filter which 
is yellow only, is, that the picture at the back focussing plane is nearly 
as visible as one passed without a colour filter. A green filter is 
in this respect not so objectionable as an orange-red filter, and when 
using the latter filter it is sometimes impossible to focus properly, 
specially so when badly illuminated; and as a rule the focussing has 
to be done at the top focussing plane. 

The yellow reflector, coloured in the mass, will absorb the actinic 
blue-violet light rays, therefore no blue-violet rays from the second or 
back surface of the reflector filter can be reflected to the top focussing 


‘ ), 7 HEN referring to one exposure cameras with one reflector 


a 


FILTER ARRANGEMENT 55 


surface, where the somewhat diminished, but in no wise altered. 
light rays from the first reflecting surface, will in this case alone 
impinge themselves on the photographic plate or plates. 

A green, that is, a minus red light filter, in place of an orange 
red reflector filter, has been recommended, in which case the re- 
flected light has to pass through an orange red filter placed, in front 
of the focussing plane, before it can be permitted to act on a panchro- 
matic plate, that is the only place, where in this filter system a minus 
blue negative colour record can be obtained. 

The green filter passing blue, green and yellow light acts in 
this formation on two plates placed face to face at the back focussing 
plane. First, the blue light will act on an ordinary plate furnishing 
the yellow negative colour record, and second, will also act on a 
colour-sensitive plate at the back, which is receiving the minus red 
light giving the red negative colour record. 

The top plate in this filter system will require about four to 
five times as much exposure as the two plates at the back, and under 
such conditions the one exposure is impossible ; it is then that the 
loss of light by the reflection can by new means be improved. 

There is a third filter arrangement, that of using the reflected 
light to act on an ordinary plate in the top focussing plane, obtaining 
thereby a yellow negative colour record only. 

The light transmitted through the yellow reflector filter, that is 
the light more or less minus blue, according to the density of the 
yellow filter, falls on two plates on the back focussing plane. The 
two plates are film to film, the first plate has to be yellow sensitive 
to furnish the red printing nagative, and the same plate has also to 
be coloured so as to act as filter; the so filtered light will act on a 
red sensitive back plate, which latter gives us the blue negative 
colour record. 

I find that this filter system permits me to take my three nega- 
tives with a fairly good colour selection in half the time necessary as 
when using an orange-red reflector filter. 

It is always possible to balance the plates in the back focussing 
plane with the plates in the top focussing plane. With an orange 
red reflector a plate having a rapidity of 120 is to be used for the 
front top plate, and a plate of 200 for the back top plate, and now 
with the yellow reflector filter a single top plate of 200 can be used, 
that is, this system permits of more rapid exposures. The ‘trans- 
mitted light is, however, of such a volume that a certain difficulty 


56 COLOUR PHOTOGRAPHY 


exists in finding a good slow plate of the right quality for receiving 
the light as front plate. Certain dyes embedded in the plate will 
do that. 

As for the reflector filter I have taken it for granted that the 
surface of the glass plate acts as reflecting surface, a surface with a 
constant reflection and not difficult to keep clean. It has, however, 
been recommended to silver or platinize the surface to augment the 
volume of reflected light. This is absurd, for the surfacing will 
diminish the transmitted light considerably, in fact the metals can 
be put on so thickly that no light passes, but the metal surface cannot 
be of less substance as to allow the polishing up. If thinner and 
varnished an irregular surface is introduced, nor is a varnished sur- 
face a more brilliant reflecting surface than is furnished by the 
ordinary glass. If the silvering is applied to the back-surface of 
the reflector filter we strengthen the secondary picture, etc., etc. 

Such a remedy gives no reliable and stable conditions to any 
one-exposure camera system. 


a a 


LIGHT FILTERS : THEORETICAL S7 


Cle BAMBERG ON HEL 


Poor il TERS : THEORETICAL. 


colour screens. To me “ light filters ” seems to be the right 
term, but colour filters is the term favoured by the expert, 
and to be correct should have been called ‘‘ coloured filters.” 

Everyone has seen stained glass interposed into some light 
tays. For example, red glass in the passage windows, or the dark- 
room windows of the laboratory. In this one case the transmitted 
light in the room will be red and seemingly no yellow or blue is 
passed. A label printed in orange-red or any orange-red object 
viewed in this orange-red light will appear white and blue will be 
black, and that is perhaps the reason why some colour-plates are put 
on the market in boxes having labels in white and red or black and 
blue, so that you cannot see the contents label on the box, when in the 
dark-room. This phenomenon represents exactly the position and 
action of a light filter in a photographic camera, but instead of the 
human eye, it is the light-sensitive plate at the back of such filters 
which records the impression. We have to remember, however, 
that the photographic plate will see only certain lights and only act 
so far as it is not colour-blind: It is in some way on this colour 
blindness, that photography in three colours by the subtractive or 
printing method of colour photography depends. 

Some photographic plates see only blue, some blue and yellow, 
some the full length and others only part of the spectrum, and by 
means of coloured glass or films, we are able to eliminate or render 
non-recording certain colour rays. We call such a coloured glass a 
light filter, and the action itself that this light filter performs is 
called absorbing the colour rays, which action imparts, therefore, an 
enforced colour blindness to the plate, where the latter without such 
filter protection would see. 

For colour photography by the subtractive method we require 
a blue, a yellow and a carmine-red (pink or rose) printing record 
according to the density of the colour. 


(ests filters are also called light filters, light screens and 


58 COLOUR PHOTOGRAPHY 


To obtain the blue printing record, the negative must be covered 
by the yellow and rose rays, that is, an orange-red filter must be em- 
ployed, which will pass only its own colours, of which it is composed, 
that is, from yellow to the ultra-red. If now the plate is a Cyanol 
plate we can use a lighter and much more yellow filter; if we use a 
plate of the Pinachrom type, then the filter must be a little darker, 
and if we use a Cyanin plate then the filter must be dark orange-red, 
or deep scarlet. 

To obtain the yellow printing colour record, the blue rays and 
the rose or red rays, with the exclusion of all yellow, must pass the 
filter. The latter is therefore of violet-blue colouring. If, however, 
the sensitive plate does not see yellow, then obviously no filter 
would be required, and a filter in that case would only retard the 
light action. 

Again, if we desire to form a red printing plate, then the res- 
pective red must be transparent in the negative; blue and yellow 
must be passed by the filter and both these colour rays must act on 
the negative, which is done by a green filter. If we use a plate that 
does not see red, then no filter seems to be required, that is, however, 
not quite true to practice. The blue rays act always much more 
than the yellow (or even red) rays, therefore the blue has to be 
damped down, so that blue and yellow record to about the same 
density, and we arrive at that by using an adjusted yellow filter ; to 
add blue to such a filter to make the same green, and therefore more 
visible and agreeable to the eyes, would be of no consequence what- 
soever, that is, as I said before, if the plate does not see red, which 
is the case when a plate is used sensitized with Erythrosine. 

It is seen by this that if we use three panchromatic plates, then 
absolutely correct filters are required. If, however, we use three 
different colour-sensitive plates: a blue-sensitive, a blue and yellow- 
sensitive and a panchromatic plate, then a much greater latitude 
in the use of light filters is permitted. 

Three different colour-sensitive plates is a necessity for one- 
exposure one-reflector cameras, not only the colour-sensitiveness 
but also the different rapidity of the plates has to be adjusted for 
such camera work. 

In a one-reflector camera, in which the reflector filter is orange- 
red, the reflected light acts first on an ordinary dry plate, say of 150 
rapidity. This dry plate itself acts as a slight light filter, nearly 
sufficient when using electric light exposures (open arc), yet not 





LIGHT FILTERS : THEORETICAL 59 


strong enough to keep back the blue activity sufficiently by day- 
light exposure, and has therefore to be coloured yellow. The 
back plate, which is placed film to film to above plate, is of a rapidity 
of about 250 and has to be sensitized with Erythrosine. The trans- 
mitted light acts through the orange-red reflector filter on a pan- 
chromatic plate, having a rapidity of about 80; thus the three plates 
are adjusted and receive about the same amount of exposure. 

I wish to mention here a war-time use of light filters, which 
were introduced as sight filters. A fluoresceinate or Uranin-coloured 
gelatine film aids the eyesight wonderfully. Freshly turned earth 
is at once differentiated, and the slightest flesh tint is enhanced in 
strength, becoming more visible even though the object is sheltered 
under the tree. An aeroplane, slightly coloured with this dye, be- 
comes at once very visible and is as distinguishable as if coloured 
pink when viewed through a gelatine film stained with crystal-violet. 


60 “COLOUR PHOTOGRAPHY 


CTLA Pat Roa Exe 


MAKING OF LIGHT FILTERS 


cameras, but also in three-exposure cameras, so I think it is 
not out of place to take here both systems under review. 

When taking three-exposure negatives and we desire to place 
the light filters near the photographic dry plate we can use ordinary 
fixed-out dry plates, afterwards coloured, and all three so-made 
light filters have to be of the same glass thickness. 

If the exposure is made through a light filter placed near the 
lens, or if the filter has to act as reflector filter in a one-exposure 
camera, then parallel plate has to be used and as a whole the com- 
mercial article called patent plate is quite correct enough when used 
for light filters. 

The commercial houses coat these filters by machinery, the 
colours being mixed with the gelatine before coating, and it is 
claimed that such filters are absolutely correct, and that bathed 
filters are bad. This statement is more than one-sided, it is com- 
mercial embellishment. I myself prepare all my filters, coat the 
patent plate first with plain gelatine and when dry bathe it to 
the colour and intensity required or desired. This method permits 
me to make one filter without waste of material. 

For separate exposures the filters have to be double plated and 
cemented. For one exposure the colour film has to be affixed to 
the back surface of the reflector filter and has to be protected from 
dampness and injury by a protective varnish; for this a cold- 
flowing shellac varnish is to be recommended. Certain varnishes 
and specially celluloid varnish form irregular colour patches. 

To cover the plates with gelatine, we require measures and a 
level position. The measure is by preference a spoon holding a 
certain amount of solution to cover a certain amount of surface. 
My best results were obtained with a 7 per cent. solution of photo- 
graphic gelatine, 8 ccs. solution to I00 sq. cm., or one quarter ounce 
of solution on an English quarter-plate. The level position should 
be obtained with a plate-glass resting on three points adjusted with 


(J arnens, bs light filters are not only used in one-exposure 


OO A a ee 


MAKING OF LIGHT FILTERS 61 


the aid of a spirit level. The room in which the coating is performed 
should be dust-free and warm ; the warmer the room the more even 
and glossy the dried gelatine film will be. The warm gelatine 
solution before coating should be filtered through three or four 
thicknesses of finest muslin, and all vessels and utensils should be 
made warm, for which purpose a warm water-bath is advisable. 
The spoon, when the gelatine solution with its aid is poured on the 
plate, can assist in spreading the solution, care being taken not to 
form air-bubbles. When the plates are coated, they are protected 
from dust with a clean glass cover, leaving an air space between the 
two plates. 

A good plan is also to place the whole levelling arrangement 
in a horizontal cupboard, one end open to let the warm air enter, 
the other side connected with a flue, into which a small lamp has 
been placed to create a gentle and constant current of air. 

For colouring the fixed-out or gelatinized plates very few colours 
are required ; they must be of the class which colour animal matters, 
gelatine and wool, and not dyes which colour only cotton. They 
must also be soluble in water, fast and permanent to light. 

To ascertain if your dye is right, make a dilute solution, acidify 
with a little acetic acid, expose one half in a test tube to the sun; if 
after a few days the colour still corresponds with the other half 
Kept in the dark, your dye is quite all right. 

Violet crystals, patent blue, methylene blue, acid yellow or 
tartrazine, crystal scarlet, fast scarlet, naphthol green, make a good 
colour selection. The colour solutions, if made from acid dyes, 
should be slightly acid, 3-5 drops of acetic acid to 100 ccs. solution 
is about right, and the concentration should be 2:100 if used for 
double-plated filters, but if used for single-plate filters for one-ex- 
posure cameras a 3 per cent. solution may be advisable, where such 
concentration can be obtained. 

Fast scarlet is mentioned above, and for such I recommend 
diamond scarlet for wool (also diamond peacock blue and diamond 
yellow) ; it is an American product easily obtainable in small packets. 

English scarlets are at present only obtainable by the ton, and 
only so if you are shareholder of the dye manufacturing company. 
The orders from an outsider are not accepted, and middlemen 
looking after the small wants do not exist. Most English scarlets 
are not permanent. The fast scarlet gives a very good filter and is 
better than a scarlet bath made by mixing Eosin and yellow. 


62 COLOUR PHOTOGRAPHY 


As a whole mixed dyes will not stain gelatine according to the 
shade of the mixture; dye testing for this purpose is done by 
flowing a few drops on plain gelatine-coated plates. Yellow in a 
mixture stains quicker than the darker dyes, and also when washing 
a film stained in a mixed colour bath, yellow will wash out before 
the other dyes. 

This antagonism of two dyes to colour harmoniously together, 
or with equal intensity, may explain certain anomalies found when 
mixtures of different colour sensitizers are used in bathing the 
bromide plate, where also the characteristics of one sensitizer will 
dominate over the other. 

To transform your gelatine plate into a light filter, immerse about 
ten minutes; if coloured too much the surplus can be washed out. 
Some colours wash out more quickly than others, so it is advisable 
to use unmixed colours where possible. But for one example, one 
plate patent blue and one plate yellow form the best possible double 
plated green filter, such as cannot be obtained with a combined bath. 

The gelatine plates when bathed in the colouring bath have 
to be rocked and moved, so that the colouring matter is absorbed 
equally by the gelatine, and when sufficiently coloured the filter is 
washed in a dish or under the tap until all greasiness has disappeared, 
and the plate is stood up to dry. Ifa film is coloured too much in 
ten minutes, it would be better to dilute the colour-solution, than to 
shorten the time of immersion. All colouring should be done at a 
specific temperature, say 65° Fahr. 

After fixing out a dry plate and also after colouring a plate, it 
should be cleared of surface dirt, by very gently rubbing it over with 
the finest and softest sponge or medically cleaned wool and rinsed 
before the plate is put up to dry. 

Double plate filters should be cemented with Canada balsam, 
the latter and also the plates being slightly warmed. When the balsam 
is thoroughly liquid a sufficient amount is poured on one plate without 
forming air bubbles, when the second plate is pressed gently into 
contact. Clips are then applied to hold the two plates in contact 
and position till set, when the surplus or oozed-out balsam is cleaned 
away, for which purpose a rag dipped in paraffin oil will do good 
service, preventing the stickiness. When cleared of balsam and oil 
the double-plate filter is bound with a paper edging in the usual way. 


PLATES FOR ONE-EXPOSURE CAMERAS 63 


TAP eRe ox Ne 
PLATES FOR ONE-EXPOSURE CAMERAS 


reflector filter to the back focussing plane, the orange red or 

scarlet filter is attached to the back of this reflector; therefore if 
we place a red sensitive plate in the focus we obtain a negative, dis- 
placed about one glass thickness to one corner, but practically in the 
usual position, just as in any other photographic camera. The 
negative so obtained is a colour record to be printed in blue. The 
light filter absorbing a fair amount of light, the exposure will be about 
24 times longer than when the exposure is made without the filter, 
but to balance the three plates for correct exposure, the rapidity of 
this red sensitive plate at the back is about 80 Watkins, if prepared 
with Pinachrom or Pinaverdol mixed with one third of Pinacyanol. 

From the same reflector filter the light, without losing any of 
its original properties, is reflected to the top focussing plane, but 
actinically this light has lost about 88 per cent., so that only about 
one-ninth part of all light that enters the camera is at our disposal 
to form the colour-records at the top. 

The first plate at the top is inserted the reverse way, to receive 
the exposure through its own glass, before it can act on the photo- 
graphic coating, and we obtain when developed, a negative having its 
parts in the same position as the negative taken direct by the trans- 
mitted rays. This bromide plate having a sensibility of about 180 
Watkins is an ordinary dry plate, but is made more transparent, 
having a coating of only two-thirds of the usual thickness. The 
ordinary plate is only blue sensitive and will furnish a correct colour 
record for yellow. This same bromide plate, without altering its 
original blue colour sensitiveness; is also transformed into a light 
filter ; it is in itself a slight yellow filter, but for our purpose not 
sufficiently yellow and has to be improved by the following colour 
bath : 

For Daylight Exposure: Filter Yellow 1: 1000 Sol.=100 ccs. 

Water TSOm 

Pomeriecuic light: Filter Yellow 1: 1000 Sol.= 75" —, 

Ammonium picrate $ per cent.= 25 ,, 
Water soa aes 


ie a one-exposure camera, the light is transmitted through the 


64 COLOUR PHOTOGRAPHY 


An immersion of two minutes stains the plate sufficiently. 
The plate is then taken out of the bath, and the surplus 
of liquid swung off the plate, which is then put away to dry. 

Before inserting this plate in the dark slide, the glass side must 
be properly cleaned. There are other yellow colours that could be 
used for the above purpose; to my knowledge no yellow which 
dissolves easily in water, say with more than half per cent., imparts 
any colour sensitiveness. Certain yellows reduce, others seem to 
accelerate, the passing of the light through its gelatine film, and it is 
the quality of the latter sort which enables me to properly expose 
a second photographic plate or film, placed in contact, film to film, 
with the yellow-coloured front plate to obtain the last negative 
colour record. 

This last flexible, or preferably solid, plate just mentioned is 
a gelatine bromide plate of a rapidity of 250 Watkins and has to be 
sensitized with Erythrosine, the negative colour record so obtained 
being printed in pink. The Erythrosine plate does not see red, 
hence no filter to absorb the red is required and the little yellow 
in the front plate is quite sufficient to damp down the predominant 
blue actinity. 

The last negative obtained is a reversed one to the others, and 
if on a thin support, can be printed from either side. If the negative 
is required for three-colour carbon printing, it has to be remembered 
that a flexible plate on celluloid basis is liable to shrink, and is certain 
to do so in a month or two ; also that a solid plate has to be printed 
through the back, and if parallel light rays are used for the exposure 
no material unsharpness will be introduced into the print. 

In making lantern slides a reversed negative is of undoubted 
advantage. 

When exposing the photographic dry-plates in the dark slide, 
and a flexible plate is being used, the same is pressed in to intimate 
contact with the front or filter plate with a card followed by a glass 
plate at the back, and a strong spring attached to the dark slide 
shutter, should give the necessary pressure from the back. This 
shows the necessity of single dark slides for one-exposure, one- 
reflector camera work. 


COLOUR SENSITIZING 65 


ADL Rex: 


SBOLOUR SENSTPIZING 


URIOUSLY enough it was the old English gelatine dry 
(Js existing before Bennett, the watchmaker, of Worthing, 

discovered by accident the benefit of the warm digestion 
method, and before Monkhoven recommended the addition of alkalis 
to the emulsion—these gelatine plates being at that time on the 
market, and I think Maddox was one such manufacturer—which 
gave Dr. H. W. Vogel in Berlin the clue to the possibilities of colour 
sensitizing. 

In the year 1873, when the wet collodion process was at the 
height of its popularity, Vogel tried to find out what action the 
spectrum produced on bromide of silver films, and when examining 
an English gelatine dry plate he found it had been stained yellow 
by the manufacturer—obviously for the purpose of preventing in- 
ternal reflections. He noticed a marked difference of sensibility to 
the different colour rays, and he forthwith proceeded to investigate 
the matter to good purpose. The action of Cyanine and Eosine he 
discovered in 1875, but it was only in 1885 that he published his 
full researches, made with modern Gelatine Dry Plates, 
discovered 1878/9. 

To-day Dr. Koenig, in connection with the Hoechster Farb- 
werke, has made sensitizing dyes his special study, and when buying 
these dyes you are informed, that full instructions how to use them 
are supplied. 

For colour photography with the one-exposure camera I find 
that only Erythrosine, Verdol and Cyanol are of utility and a 
short description how to use them may be welcome here. The 
original formula was something as follows :— 

To 500 grammes of distilled water add 15 ccs. 1 : 1000 Erythrosine 
stock solution and 2 ccs. of ammonia, or 10 ccs. Verdol or 
Cyanol (or a mixture of these two dyes) stock solution as sold by the 
makers and I cc. of ammonia. It has been recommended to add 
potassium carbonate to the sensitizing bath instead of ammonia 
and 20 ccs. of a I : 1000 potassium carbonate solution can be added 
o the Verdol solution, instead of the ammonia, with advantage, 


66 COLOUR PHOTOGRAPHY 


but such addition to the Erythrosine bath would be the cause of 
complete failure. 

The dry plate is first soaked for one minute in a plain alkaline 
water bath, the alkali being the same as that of the sensitizer, directly 
followed by the immersion in the sensitizer for three minutes. 
The solution must, however, be kept on the move at intervals, or 
unequal sensitizing will be the result. The plate after sensitizing 
should be washed in running water for another five minutes, then 
the surplus is swung off and the plate put up to dry. 

The above Verdol solution is sufficient for half a dozen half- 
plates, but not more. The last plate showing about half the colour 
sensitiveness of the first. 

The Erythrosine bath can be used much longer, the dye being 
water soluble. 

It has also been advised to make up the sensitizing solution 
with half alcohol and half water. Such an alcoholic bath lowers the 
rapidity of the plates considerably and the addition of potassium 
carbonate to an alcohol bath is a positive drawback, also a very 
questionable help with the Eosines. 

Cyanol, Pinachrom, Pinaverdol are soluble in alcohol— 
the stock is a pure alcohol solution—and if added to water, in which 
they are not soluble, they will slowly be thrown out, forming a sort 
of colour scum on the border of the porcelain dish when sensitizing. 
Each successive plate, sensitized in such a bath, can therefore take up 
only a more and more limited amount of sensitizer, so that no two 
plates sensitized one after another are alike in colour sensitiveness. 
It is, therefore, obvious that the addition of a certain amount of 
alcohol, that is, just such an amount as prevents the above men- 
tioned throwing out, must be a beneficial one, helping towards a 
uniform production. By experimenting I found that 15 to 20 per 
cent. of alcohol is about the right amount to hold the colour sensi- 
tizing dyes for a sufficient time in solution. This amount of alcohol 
is also sufficient to accelerate the drying of the bathed plates, and in 
case of the Eosines as well as of the Cyanins and their derivates 
helps to give clean plates ; it also saves time. No preliminary bath 
and no after washing are required. | 

In a litre of such an alcoholic Verdol bath I have sensitized 
two dozen 12 by Io inch plates, and on inspection by daylight I found 
the bath still fully coloured, and looking in a better condition, than 
the first-named water bath, in which two plates only had been bathed. 


COLOUR SENSITIZING 67 


An alcoholic Erythrosine bath can be used again next day after 
filtering, but not so the Verdol bath, which is more liable to be 
decomposed by the organic matter, and as a whole it is the best 
course to use a freshly-made solution, not using a bath after it has 
stood longer than two hours, which time is sufficient to form a floating 
scum or deposit. 

To impart a proper colour-sensitiveness with an alcoholic 
Erythrosine bath (or Eosine bath) more ammonia must be used than 
with a water bath, but with the Cyanines, Verdol, etc., the am- 
monia can be dispensed with. The advantage is a cleaner and 
slightly slower plate, which latter, if desirable, can be picked up 
again by giving the plate an ammoniated fumigation in a special 
box or cupboard. 

Ordinary water can be used for the colour bath if no ammonia 
is added, but ordinary water boiled with a little ammonia and filtered 
when cold and settled, can always be used. 

The alcoholic stock solutions of Verdoi and other Cyanines 
are I : 1000 as sold by the makers. 

The stock solution for Erythrosine is a two and a half per cent. 
water solution keeping indefinitely. 


The sensitizing bath is Stock solution 15 ccs. 
Alcohol 1508s; 
Water 820 4, 
Ammonia (if re- ES pees 
quired) 


For colour-sensitizing, pure bromide plates must be used, 
especially for Erythrosine. Nearly all English dry plate makers 
add carbonate of ammonia, and such like chemicals to the emulsion 
before coating, with the belief that the plates will be more rapid 
and softer working. All such plates are of no use whatsoever to 
colour workers, who have to, or desire to, sensitize dry plates for 
colours ; and plates with an acid alum or chrome alum substratum 
destroy the sensitizing dyes. 

The plates should be protected from direct dark-room light 
when sensitizing, and perfect darkness for the preparation of red 
sensitive plates is advisable. When handling the plates, do not 
do so by holding the plate up between two fingers, and so allow the 
saline perspiration from your fingers to mix with the adherent 
sensitizer and then have the mixture run diagonally over the 
plate. 


68 COLOUR PHOTOGRAPHY 


The sensitized plates should be dried in absolute darkness 
and the process should be finished under six hours. 

It is a well-known fact that colour-sensitized gelatine dry plates 
will not keep ; if you wish to depend on regular sensitiveness it is 
advisable to sensitize at home, say once every month, and for that 
purpose a dust-free dark-room is required, and one which can also 
be ventilated and warmed. I find there is nothing better for the 
purpose than a gas stove, one of the box-form cookers, the fumes 
being carried away by pipes into the chimney, and the free light and 
air passage below bricked up so that the air is allowed to pass only 
through a winding passage. 

The prohibitive price of Alcohol has lately induced me to use 
Acetone. I find an Acetone bath of twenty-five per cent. much better 
than an Alcohol one, specially so with the red sensitizers, less so for 
Eosine which seem to decompose or alter its colour. All plates are 
perfectly free from scum, even with Cyanol, but a slight overdose 
of Ammonia makes for fog. It is worth while to investigate further 
in this direction.* 








* Dr. Arthur Hubl has shown that whilst some dyes have their 
sensitiveness augmented by the addition of alcohol, their sensitiveness may 
be destroyed by using a solution too strong in alcohol. The addition of 
ammonia, he says, gives a slight gain in sensitiveness provided that not 
more than one or two drops of ammonia to too cc. of both is used.— 
Photogr. Chrontk. No. 6, 1920, pp. 41—43. (W.G.) 


— a ono 


CORRECT COLOUR REPRODUCTION 69 


inte Ree XTi. 


CORRECT COLOUR REPRODUCTION 


wrong with the filters as usually described and sold. 

In a general way we say that an ordinary plate for a 
yellow record needs no light filter, because such a plate sees only 
blue. Now I am going to contradict that statement, because my 
photographic records tell me otherwise. I have found that the 
ordinary gelatine bromide of silver plate not only sees blue, but 
also red and certain yellows. I must naturally qualify the reds ; 
they are specially the Eosine, Erythrosine, Magenta, printing red and 
similar colours, which are practically missing in the spectrum; in 
the latter the visible red seems to be similar to our filter red, deep 
scarlet and orange red, colours which the painter can only obtain by 
adding yellow to the just mentioned Eosine colours. 

Now all these orange-like colours, these spectrum reds, will 
not record in the negative, they will show the same as yellow, that is, 
will be transparent in the negative. 

On the other hand all the reds minus yellow, the Eosine series, 
will record exactly like blue, that is, show opaque in the negative. 

For my explanation I classify the yellows into “ ordinary ” 
and ‘‘ special” yellows. To the latter belong all those which do 
not cut from the violet, but from the yellow green end of the spectrum, 
and these, when photographed by an ordinary plate, return a record 
just like the blue. See No. 1, Fig. 30. 

This defect is not eliminated when using a blue-violet light 
filter in conjunction with a panchromatic plate. But this special 
yellow can be made to record correctly in the ordinary bromide of 
silver plate by inserting in the light path a light yellow filter. I use 
an isochromatic patent plate as sold on the market. 

The second negative colour record, taken on an Erythrosine 
sensitized plate, is supposed to see yellow and blue only. This 
statement is not quite correct, because such a plate sees all colours 
except filter red (spectrum-red, scarlet and deep orange). Yellow 
green also is not recorded so well as blue green. To make this 


[wrens are times when I feel as though something were 


70 COLOUR PHOTOGRAPHY 


Erythrosine plate serviceable, I require a yellowish light filter, a 
filter whlch slightly cuts down the blue activity in the violet end of 
the spectrum, when the Eosine series will become more transparent 
in the negative ; therefore the printing qualities will be improved, 
because the printing red, the red minus yellow in the red colour 
record can now be printed. 

If a red negative printing record is to be obtained, by means of 
a panchromatic plate, the light filter has to be green, Naphthol green in 
preference. A filter minus red must also cut out the extreme violet. 
If violet is of the same density as blue, as many green filters permit 
of, how will you obtain a violet in your print without the necessary 
red ? 

Now we come to the third negative colour record, the blue 
printer, for which we use an orange red filter in conjunction with 
a panchromatic plate. As a rule the filter is too dark, so that blue 
and green are rendered alike in the negative. The red sensitiveness 
in the modern panchromatic plate is such that violet and the Magenta 
colours are recorded of the same density as Eosine or orange. This 
negative has to be printed in blue and if for violet and magenta the 
blue forming part of such colours is opaque in the negative, how 
will you obtain these colours ? 

For that very reason I prefer a Pinachrom or Pinaverdol plate 
if a very rapid exposure is not required, because such a plate would 
not so quickly be over-exposed in the extreme ends of the spectrum 
and therefore leave violet and magenta more transparent in the 
negative record. 7 

All the experiments refer to exposures by daylight. The 
negatives so obtained are of a mellow appearance, whereas artificial 
lights are apt to render the same somewhat harsher and cleaner, 
through under-exposure in the shadows. 

I have found an artificial spectroscope of great help. It is 
formed of a series of coloured gelatine films. These are dyed with 
Violet crystals, Methylene blue, Patent blue, Acid-green, Naphthol 
green, Acid yellow, Uranin, Filter red, Eosine, Xylen red ; the latter 
could be replaced by Fuchsin. 

The effect of an exposure without a filter on an ordinary plate 
is shown in the first record in Fig. 30; a like result is obtained with 
a crystal violet filter. 

An acid green filter, a signal green glass or a light isochromatic 
screen cuts out more of the yellow as shown in the second record. 


CORRECT COLOUR REPRODUCTION 7! 


1. Ordinary plate. No filter. 


2. Ordinary plate. Iso filter. 


3.Erythrosin plate. No filter. 


4. Erythosin plate. Signal glass. 


5. Erythrosin plate. Iso ffter. 


6. Erythrosin plate. Naphthol 
green filter. 


7. Cyanol plate. Orange filter. 


8. Cyanol plate. Orange filter. 





‘ Fig. 30. 


72 COLOUR PHOTOGRAPHY 


With a methylene blue or patent blue filter a result is obtained some- 
what between the two. 

It is also worth knowing that when interposing a yellow green 
or naphthol green filter into the light cone impinging on an ordinary 
plate the four top fields only would be exposed. 

Speaking now of an Erythrosine plate and exposing such to 
direct light without the interposition of a filter, the result will be 
like the third record, all colours registering with the exception of 
the orange red. 

A crystal violet filter will give a good yellow colour record 
similar to picture 2. The yellow record is less pronounced if ex- 
posed through a patent blue filter, and a signal green depresses the 
Eosine too much, to the detriment of the yellow as shown in the fourth 
picture. The fifth record shows the effect of a light Iso filter, and 
giving as good a colour record for red as could be desired. A yellow- 
green glass or a naphthol-green filter of middle density gives a some- 
what exaggerated red printing record, showing that a light naphthol- 
green filter is a quite sufficient filter if used with such a plate. 

The last two records are made by exposing a Cyanol plate 
through an orange filter. If pure Cyanol is used the plate pre- 
disposes greatly to solarization in the red high lights, whereas a 
Cyanol-Pinaverdol plate is free from that defect if no ammonia is 
used. | 

If a slight loss of light is of no account then a Pinaverdol plate 
is much to be preferred ; such a plate will correctly record the blue 
tint in the field next to the neutral tint, while the Cyanol plate 
produces the same result as Eosine. 

A Pinaverdol plate obtained without ammonia in the sensi- 
tizing bath is very slow; the sensitiveness is increased about five 
times with ammonia, when it will be about two-thirds that of a Cyanol 
plate, the latter being sensitized without ammonia. 

The last record shows the effect of under-exposure. It amounts 
practically to a false colour rendering, a thing that can be obtained 
with the best of plates and filters and shows the value of standar- 
dization, the necessity for the operator to know his light, plates 
and filters. . 

The search for “ absolute” filters with which any so-called 
panchromatic plates will give perfect results in the hands of a me- 
chanical worker cannot be complied with. They do not exist, and 
the £1,000 offer for such is only an invitation to be swindled. 


BALANCING OF FILTER AND PLATES 73 


CHAP DER XXIIT. 


BALANCING OF FILTERS AND PLATES 


E have in aniline dyes the means to filter out some lights. 

W\ Generally speaking the light that passes the light filter, and 

reaches the eye, will in the major part also prove to be the 

active part of the light passed. The rays that will not pass through 

the filter cannot act on the plate, and the plate will show this 
imparted colour blindness as printing quality. 

Generally speaking, if in a light filter certain colour rays, which 
we desire recorded on a photographic plate, cannot pass, we have 
to augment that colour in the filter; or if the filter is already too 
denise, we have to diminish the predominant colour. Further, if 
the colour-sensitiveness of the photographic plate is less in one part 
of the spectrum than in another part, for one colour than for another, 
we can partly correct this depression or gap, by passing more com- 
pensating light rays of that respective colour through the filter. 

I mentioned before that the printing quality is the principal 
thing for us, whereas just the opposite qualities form the principal 
requirements for the transparency or additive method. The reason , 
is because in this latter, we take with a blue-violet filter a negative, 
which records the blue-violet colour rendering by opacity, and this 
in the glass positive will therefore become transparent, so that when 
projected by the aid of a blue-violet filter it will show blue violet ; 
the same applies to the green and orange-red records. — 

But for the printing or subtractive method, the negative for 
the blue record is obtained through the orange-red filter—a filter 
minus blue. The green filter negative gives the pink records and 
the violet blue absorbs all yellow to enable a yellow print to be made.. 

In my illustration (Fig. 31), I try to show the relative action be- 
tween plate and filter in reference to the subtractive method. We 
must also keep in mind, that if the colouring of the filter is too weak, 
not enough undesirable light rays are cut out, and the print will not 
show the full density of the colours desired. A similar defective 
colour effect would be produced by the want of contrast in the 
negative. 


74 COLOUR PHOTOGRAPHY 


400 430 490 535 590 660 690 


vie ' Blue ‘Gr iYellow' Orange. Red ' 
‘ 


Blue filter. 
Ordinary plate. 
Negative. 
Yellow print. 


Yellow filter. 
Erythrosin plate. 
Negative. 

Red print. 


Yellow filter. 
Orthochrome plate. 
Negative. 

Red print. 


Green filter. 
Erythrosin plate. 
Negative. 

Red print. 


Orange filter 
Pinachrome plate. 
Negative. 

Blue print. 


Orange filter. 
Cyanol plate. 
Negative. 
Blue print 


Yellow print. 
Red print 
Blue print. 





BALANCING OF FILTER AND PLATES 75 


My illustration shows in each of the different sections, the 
absorption of a filter, the photographic plate and its colour sensitive- 
ness, the negative recorded, and the print obtained. The filter 
shows the absorption; the plate, the colour blindness; the negative, 
the transparent parts ; and the print the residue as printing quality ; 
all indicated by the dark spacings. 

Section “a” shows the action of a blue filter on an ordinary 
dry plate, which latter is also called the blue plate, being sensitive to 
the blue rays only. This blue sensitiveness is relative only, because 
with any other filter and much longer exposure, any other negative 
colour record could be obtained with it. A violet filter would pass 
a little more red, which would show when using a panchromatic 
plate. The different sections, b, c, d, e, f, g, explain themselves ; 
the last section shows the three colour selections required for three- 
colour printing. 

We are told by some authorities that with a spectroscope it is a 
perfectly easy matter to adjust all filters, and that without such a 
costly apparatus we are unable to find the proper filters and plates. 
Such a dictum I cannot accept as I have tried different means— 
means that were already indicated by an earlier worker, A. von 
Hubl. Moreover, a complete spectroscopic, or, in other words, 
theoretic adjustment is to my idea not possible when using one- 
reflector cameras ; we can only use a practical adjustment. 

To adjust all filters and harmonize them with the plates, I re- 
commend the use of a colour chart, such as can easily be made with 
Methylene blue, Patent blue, Naphthol green, Acid-yellow, Uranin, 
Orange-yellow and Filter red and Pink ; or again the colour printers’ 
standard colours can be used for the same purpose. White paper 
must be used as support and colour must be applied to saturation. 
If some dead black, platinum-grey and white are also represented in 
the chart, then we are every bit as well equipped, and it is also 
cheaper than using a spectroscope. We simply photograph this 
chart and the resulting negative will reveal all.we desire to know. 

This shows the necessity of harmonising plates and filters 
together. The best of filters used with a wrong or unsuitable 
plate may not give the result you require, so “ verify ” and don’t 
accuse others with your own want of understanding. 


76 COLOUR PHOTOGRAPHY 


CHAPTER? XociNs 


EXPOSURE. 


we have only an ordinary photographic camera with three 

single dark slides to experiment with, and we desire to use 
this camera for such a purpose, then we charge one slide with the 
blue filter, and an ordinary gelatine dry plate, which is blue-violet 
sensitive only, in preference ; in the second slide we place a light 
green or light yellow filter and an Erythrosine plate and in the third 
slide a scarlet filter and a panchromatic plate. The light filter must 
be clean and dust-free and, by preference, should have the film side 
facing the subsequent exposure; the filter will then be less likely 
to be injured and small defects in the same will then not be too 
sharply reproduced in the negative. To keep the plates in position 
packing has to be introduced. If double slides are used the partition - 
has to be removed, so that they can be used as single slides, and the 
side on which the exposure is to be made, must be specially indicated. 

Before we are ready to expose the plates, we have to adjust the 
focussing plane, accounting for the compensating distance of the 
thickness the light filter displaces the photographic dry plate. 

For my own use I had constructed three slides, which allow 
the insertion of the light filters from one side, and the dry plate 
from the other side, having a separation between the two of 4 
centimetre. The slides carry outside also a small coloured insertion 
of the same colour as the filter inside, a precaution which gives me 
sure information of the contents. I also took care to cut out one 
notch in the separation containing the green filter, and two notches 
in the separation containing the scarlet filter, which notches will be 
self-registering on the exposed plate, and effectually prevent the 
negative colour records being afterwards mistaken. 

Before we start on our regular work, we have to ascertain the 
exposure ratio of filters and plates together, and for this purpose we 
expose a set of plates on a colour chart, as indicated on page 
70 and 75 and the negatives so obtained should show white, 


ae gain our first knowledge of colour photography, suppose 


EXPOSURE 77 


platinum-grey and black in all three records alike ; only the colours 
should be recorded differently. 

For example, my filters and plates work at the following ratio : 
Lumiere blue label plate with light-blue filter one and a half; the 
same Lumiere plate sensitized with Erythrosine and used with a 
light green-yellow filter two and a half, and the same Lumiere plate 
prepared with Pinachrom and the scarlet filter ten, or only five if 
sensitized with Cyanol. The time of exposure I find easiest with 
the assistance of a Watkin’s Bee-meter, the time required in exposing 
the same to the dark standard being about the same, as required for 
the Pinachrom plate with a lens aperture of f/10. 

If making exposures for colour work, it is essential that we do 
so only, when good light is available, because the actinity of the red 
rays in dull light diminishes more rapidly than the actinity of the 
blue rays, a point which has to be considered, when exposing with 
three-exposure cameras. In one-exposure cameras there are reflec- 
tors, we cannot do without them, and the reflected light also loses 
its actinity quicker in dull light, so that to all appearances a one- 
exposure camera which makes use of the reflected blue actinity has 
the different light actinities always more equally balanced for all 
three requirements to form three properly exposed negative colour 
records. 





Fig. 32.—Change of light in day-time. 


Suppose now we find a subject for a three-colour photograph, 
a view of a cross road in which there is a wall parting light and 
shadow (Fig. 32). If now the exposure ratio for the scarlet filter 
would be five minutes, we should require another five minutes to 
change and expose the other two slides ; say in all ten minutes are 
required to expose three plates with a three-exposure Camera, a 
time which the one-exposure camera could do in five minutes all 
told, with the same light and stop conditions. 


78 COLOUR PHOTOGRAPHY 


How this time allowance of ten minutes slips away, let me 
illustrate by the following. The travel made by the sun in twenty- 
four hours has been divided into 360 degrees, from which we can 
calculate 15 degrees in one hour or 2} degrees in ten minutes. If 
under these circumstances the shadow or light has an effectual 
distance of 50 metres, that is, from one object (the wall) on one side 
of the road to another object (the scales) on the other side of the same 
road, then our sunshine would travel at the rate of about 50 
metres in four hours or full 2 metres in ten minutes, and that 
would be during the ten minutes required to photograph a view. 

This “ change of light in daytime ” on the opposite side of the 
road, we can also calculate as being 4 centimetres at a distance 
of I metre, or I inch at a distance of 25 inches during ten minutes. 
This change in shadow and light must, of course, reveal itself in the 
finished three-colour print, and it does so by showing itself as colour 
fringes. It will show itself in the most obnoxious way when photo- 
graphing moving subjects. 

If we take, on the other hand, the same subject with a cne- 
exposure camera, these colour fringes cannot form, because the 
change of light is registered alike in all three negatives. 

If, during exposure on a landscape, the light changed partly, it 
would materially affect the three exposures, but never the one 
exposure. Only fancy the following case with three exposures, 
one negative is obtained with full sunlight, the second negative with 
the sun partly behind a cloud, the third negative with a slight smoke 
from a locomotive passing through the landscape, or only the smoke 
from a chimney top changing its direction. I am sure it would not 
be the operator taking such things who would suffer the penalty, 
but the poor printer, who relied on conscientious work from his 
predecessor. 

If we take an object for the value of its colours, we must see 
that the object is well lighted. If, for example, flowers or a short- 
distanced view is the object, then I advise subdued light, or if sun- 
light has to be used, then do not take the photograph when the sun 
is high, but at such a time when a minimum of shadows are created, 
and have the light strike the object nearly from the front, as nearly 
as possible in the same direction as you are posed towards the view. 
It is not the shadows you photograph as in an ordinary monochrome 
photograph, but the best reflections of colour from your coloured 
objects. 


EXPOSURE 79 


In judging the colour effect on your object look at it with one 
eye only, and that one eye shut to such an extent as to produce a 
diaphragm effect with the eyelids. You soon will find, in looking 
at the object, whether you have enough colour left to predominate 
over the effects of shadows, dark non-coloured objects and the 
reflex lights, and you can then draw your own conclusions as to 
fitness for a photograph in colours. We often look at a tree and 
may see only a few green spots, but because we know that the tree 
is green, we imagine we see the whole tree as green, at the same 
time the tree might be one mass of shadows, so that its colours 
would really be represented by black; therefore, remember the 
camera would more than differentiate the colour effect. 


80 COLOUR PHOTOGRAPHY 


CHAPTER XXV. 


LABORATORY 


which the temperature should always be the same, say 

65°F., so that the work can always be depended on. The 
development of colour negatives can only be carried out in 
darkness, and the lifting of the plate out of the developer, and inspect- 
ing the same by transparency, in front of the ruby glass, has to be 
discarded absolutely. 

The development has now to be done by time, and the time 
factor depends on the temperature. 

Nearly every kind of developer is serviceable, with the exception 
of ammoniacal solutions, but the Amidol developer is very good, 
when made from fresh and white powder; this developer has the 
tendency already to discolour when dry. I myself have been 
perfectly satisfied with the following developer : 

Dissolve in 700 grammes Hot water. 

3 Re Metol. 
3 oe Hydrochinone. 
20 ce Soda sulphite anhydr. 
100 os Soda carbonate, pure. 
I fn Potass. bromide. 

Store this stock solution in small bottles, holding say 25, 50 or 
7O ccs. equivalent to I, 2 or 3 ounces; when full and properly 
corked it will keep any time, and for use it should be diluted with 
the same amount of water, the bottle being the convenient measure 
for the same. 

When developing three colour negatives, taken with the one- 
exposure camera, having one reflector filter, it is to be remembered 
that one plate is reversed, and has to be placed the film uppermost 
into the dish. The operator must take care to know which plate he 
is developing, as this has to be done in the dark, because the different 
plates require different time. The blue or panchromatic plate, 
exposed through the scarlet filter, takes two and a half minutes to 
develop; the yellow or ordinary plate, receiving the first reflected 


‘ colour photographer has to have a proper laboratory in 


LABORATORY SI 


light, takes three and a half minutes and the red or Erythrosine 
plate takes five to seven minutes to develop. When properly fixed 
and washed they are surface cleaned with a swab of cotton and 
stored up to dry. Ifthe Erythrosine plate is a flexible one, care has 
to be exercised that the drying is done slowly and equally without 
distorting the same. 

It is sometimes necessary to intensify negatives ; for this pur- 
pose immerse the dry negative for a few seconds in plain water and 
then bleach in a solution made up of equal quantities of one per cent. 
potassium bichromate and half per cent. acid hydrochloric. After 
washing in semi-darkness, expose to light, diffused daylight in pre- 
ference, for a short time, and re-develop with the ordinary developer 
till fully black. 

When reducing a negative an agent must be employed which 
does not eat away the half tints, and for that purpose I strongly 
recommend the following : 


Red prussiate, freshly made 3% = I00 ccs. 
Soda carbonate stock Se On, =e lOne,, 
Minmouitmienitrate stock .. 10% = 10 -,, 
femlomde.0f sodium stock... 10% = 10 ,, 


Immerse 10, 20 or 40 seconds, rinse and fix in fresh hypo. ; 
if not reduced enough, repeat the operation, but always rinse between 
each change, never work with stagnant solutions, or unequal reduc- 
tion will be the punishment meted out to the careless worker. 

The negatives should show a fine and complete graduation, 
the densest parts, which represent white, or reflections should just 
miss being transparent. Dense negatives are no good, they give a 
false colour rendering, because parts that should show slight colour- 
ing are not allowed to act when printed and negatives which are 
too contrasty obliterate all details in the shadows. 

If you desire to clear your negatives of the white deposits from 
soda and carbonates showing after fixing, wash slightly and then 
pass the negative through a water bath to which has been added a 
few drops of acid acetic. Metabisulphite is for the extravagant. 

Safelights are recommended for colour workers, but a safelight 
is a myth if some light rays pass through it, and if no light rays can 
pass, it is absolute darkness. It is, however, possible to relieve the 
absolute darkness with the comfort of some light, and this “ dark- 
room illumination ”’ can be managed as follows. Asmall oil lamp or 


82 7 COLOUR PHOTOGRAPHY 


quite small electric lamp “‘ L ” (Fig. 33) is placed in such a manner 
in a lantern, which has an ordinary ruby glass, that the light is 
thrown along a lower bench only towards and into a box “ B,” 
having an opening which stands a short distance away. The 
light rays are swallowed up in the box and the top “‘ T ” forms a 
second bench, which is in absolute darkness and where the plates 





Fig. 33.—Dark-room illumination. 


can be handled with perfect security, so long as they are not exposed 
to the light. My lower bench can hold the watch, developer or 
chemicals. This little light is just sufficient to keep us'in touch 
with the pleasures of life, one feels not altogether buried. To be 
doubly sure of the illumination, a swinging shutter “P” with a 
smail box attachment can be fixed to the lantern front, and when 
shut down an opening ‘“‘ S ” under the small attachment could still 
illuminate the watch. Development is, and will remain, a mechani- 
cal operation performed under controlled conditions. 

I wonder if a surface prepared with luminous paint would give 
a sufficient and safe dark-room illumination for handling panchro- 
matic and other photographic plates. 

I may here add a hygienic hint respecting chemical eczema 
to which some people are subject through handling chemical 
solutions. Wash the hands often in warm water, using soap, then 
replace by chemical action the abstracted fat with an ointment made 
of lanoline mixed with a minimum of glycerine and castor oil; this is 
the best remidy I know. Velvety skin is the sign of health. Eczema 
starts with a glossy skin, having the appearance of a more or less 
horny collodion film. 


CAMERA CONSTRUCTION 83 


iA Pal Rox Vil, 
CAMERA CONSTRUCTION. 


FEW years ago a cyclopedist of all trades, but with special 
A tecorstia photographic proclivities ventured to describe 

how to build a one-exposure camera, and most accurate 
results were figured out. Now, if square areas have to be made 
to measurement, such can be fairly and accurately obtained ; 
not so if reflecting surfaces at an angle and of uncertain thickness 
come into play. Such measurement may theoretically be reckoned 
out, but the constructor is unable to follow such directions accurately, 
and therefore to furnish an instrument optically correct other means 
have to be used to attain that end. 

For a one-reflector camera a bed is required to hold the re- 
flector in its-place, and such bed has to be most accurately placed; I 
think this is the most important item to attend to, being the place 
where the refracted and the reflected light cones are balanced. Space 
has also to be given for the compensation plate and the thickness of 
_the two glasses has to be accounted for. The horizontal and vertical 
size of the focussing planes as to size of plate and length of the 
optical light-cone has some bearing in the construction of the camera, 
which must have absolutely secure, adjusted and permanently fixed 
focussing planes. No collapsible contraptions are possible, such 
outside specialities are only for the gullibles and for such pretenders 
to wisdom who do not work the instrument, but know everything 
else about it. 

The best way to make a one reflector camera is, with the help 
of a ‘“‘ constructive guide” (Fig. 34), to make a solid guide and use 
such. Say we will make such a camera for plates 3} by 44, then 
34 plus 44 is 74, which is the length of the central ray “‘ C ” passing 
to Fi, the inner focussing plane forming part of the light cone 
coming from the optical centre. 

If now we erect a line at “‘ K ” slanting at 50 degrees, this line 
will cross the exterior upper light ray at “‘ L;” from that crossing 
point we form at the same angle another line ‘““L” to “B.” This 
Riese Dor. B’- Mis the bed. “P= for the: -re- 
flector; in such a camera ‘‘ L’’-“‘ K,” if extended to “‘ G,” shows 


84 COLOUR PHOTOGRAPHY 


the direction in which the compensation has to be laid down. If 
now we cut out a solid tin or brass plate “B”-“E”-“D”- 
‘“M ” and we file into it one or two registering marks “ H ” into 






i 
Z 





Fig. 34.—Constructive guide. 
the bed-line “‘ B”—“‘M” we have a complete “ constructive 


guide ’ for making our camera, especially if our compensator line 
** Co ” is also indicated on the same 


Ries sisi sisi di ll 


NAS re a 


50° 


. 
~e~—eM Mg Mg Bg Me Me wer Ke eM Me ew ewe ee eH em ewe ee ee ee 








Fig. 35. Construction of One-Reflector Camera with Compensation. 


Referring to Fig. 35, “‘ Construction of one-reflector camera 
with compensation,” we start by squaring up the ground floor of 
our camera, inner width 4} and length 63, and then flank the same 


CAMERA CONSTRUCTION 85 


with two side-walls, inner width 63 by 63 length (plus joining up 
wood) ; when fixed lay down your “ Constructive guide ”’ on a side 
wall inside, square up with “‘ B-E-D.” Adjoining the constructive 
guide fix a temporary block, leaving an opening near the registers 
“H,” then fix a metal blade “‘ BE” upright into the side wall so 
that it projects beyond “ P,” see that “‘ B-E ” is perfectly level with 
the ground and that the upright is adjusted to “‘ E-D ” the back- 
focus F 2. Also allow for one glass thickness which corresponds 
with the displacement of the picture plane caused by the refraction 
through the two glasses. 

The next step is to remove the constructive guide, and to fix a 
strong squared bed-support from the bottom to the top, flush against 
the temporary block, having first cut out an opening, so that the 
two metal blades are not interfered with. If the bed-support is 
properly fixed with glue and screws, the temporary block is removed, 
and the construction guide is put into its place, making use of the 
two metal blades and the fixed bed support, when the top focussing 
plane “‘ T”’ is found. The focus should, however, be displaced to 
‘“< T-F,” half a glass thickness or so, to leave room for a finer ad- 
justment later on. It is to this latter distance that the side wall has 
to be planed down; the other side wall is treated exactly the same 
and both are then connected up to finish the camera. 

If the displacement of the picture plane has not been accounted 
for at the back focussing plane, the central ray can be marked on the 
top focussing plane as one thickness of the reflector towards the 
lens board. The focussing planes here given are the rests for the 
dark slides, and must on no account be further altered. 

The reflected focus is also just a shade longer, so that we are 
able to adjust the two focussing planes with packings on the bed 
support. Two points of packing force the top focussing plane 
three points further away so as to be in register with the back 
focussing plane. 

If we have marked a perpendicular line from “M” to “Z” 
on one side wall we have the place for an upright bed support which 
we fix innermost, then we connect the line with “ G”’ on the dia- 
gram of constructive guide of the opposite corner which gives us 
the guide for the compensation plate. This plate has the corner cut 
off near ‘‘ M ” so as to be able to go into its place, which is at the 
back of the reflector ; the latter is slanting from bottom to the top, 
the compensation plate is slanting from one side to the other. 


86 COLOUR PHOTOGRAPHY 


Before fixing on the guides for the slides in their respective 
places, the front for holding the reversible, or other, lens board has 
to be affixed. It is also advisable to insert a solid transfer piece from 
‘“N ” to the top, connecting the side walls, to give the camera box 
perfect rigidity, and also to exclude extraneous light from passing 
over the reflector filter to the back or to the top focussing planes. 


R set § 


O80 « 
. Laoey 
° SARE 
oes 
reat 
. * 
; 
F 
° 





Fig. 36.—Constructive block 


The compensation can, if desired, instead of after the refraction, 
be inserted (as D-C Fig. 29) parallel with the reflector into the re- 
flected light-cone (as patented by Ives in the United States of America 
for his two-reflector system only) in which case all pictures will be 
slightly distorted; also, internally reflected rays may cause some 
trouble, and may be the part origin of what Ives declares to be 
** polarized light effects.” If this latter is not entirely due to ex- 
traneous light rays, as we have seen, none of his cameras, taking 
negatives, are protected from such light infiltrations, and as no such 
protection is indicated in any of his patent specifications. No such 
references came to my view. 


Fig. 37.—Last. 


There is a second way to build a one-reflector camera, and 
that is with blocks used as last. The constructive block (Fig. 36) 
sawn into two parts on the line “ P ” will form a “ last ” as shown 
in the drawing (Fig. 37.) The proportions are the same as with 
the constructive guide. Fi and F2 are the focussing planes, the 
lens board “‘ O ” must be erected square at “‘ B ” on the line “‘B-D.’’ 


VERIFYING THE FOCUS 87 


CRAPT ER “XXvit; 


PenIPYING THE FOCUS 


approached with a view to taking an interest in one-exposure 

camera work, have declared that it is impossible to make three 
negatives of the same size when taken in more than one focussing 
plane and about half of the above number were sure that the red 
printing negatives would be out of size. Now as the red negative 
record is always obtained with one of the others, film to film in con- 
tact, how can it be of a different size from the one with which it is 
taken? That seems obvious, but the engraver is absolutely positive 
that it cannot be so. How does he come to that knowledge ? How 
does he verify ? He simply superposes the glass positives and there 
you have the complete method! He does not trouble about the inter- 
vening glass thickness. This is all so primitive that I cannot help 
being sarcastic about it, and all said and done, it is a startlingly mis- 
leading way for an expert (which they all claim to be) to condemn 
other people’s work, submitted in good faith, and trusting to honour- 
able treatment. Others, when making the glass positives, never 
thought that in reversing one of the negatives, they themselves, by 
omitting to add the compensation of the glass thickness, were making 
glass positives of unequal size from equal sized negatives. For 
this they did not blame themselves, but only the man with the one- 
exposure camera. These few words must give me the excuse for 
explaining how the experimenter should go to work. 

First, a large white sheet is placed at a certain distance before 
the camera, but so that the sheet is about at right angles to the central 
ray of the lens. The enlarged plate size is then marked on the 
sheet, then just inside the enlarged plate size two or three thick and 
two or three thin, black, horizontal, vertical and diagonal lines are 
drawn. These lines are then photographed, first on one plate in 
the back focussing plane and secondly through a blank and trans- 
parent, but slightly marked front top-plate on a second plate in the 
top focussing plane. Thus, we have one right-faced and one reversed 
negative, which when placed face to face and superposed, have no 


GQ pooroacies like fifty per cent. of the engravers who were 


88 COLOUR PHOTOGRAPHY 


glass separation between them, and will give the best possible in- 
formation about size. If the marked top plate is too large, then 
the reflecting distance has to be diminished, which can easily be done 
by placing some packing under the reflector filter on the reflector 
rest. The packing is best made with wood shavings which are 
fixed with glue to the rest. Very small differences can be adjusted 
with paper, but the same has to be of a solid and pressed kind. When 
once the two focussing planes are adjusted, they are for all intents 
and purposes permanently so, but occasionally require verification 
like everything else. A difference in size of 3 mm., through the top 
registering longer, has to be adjusted with 2 mm. packing. 

Ordinary or enlarged glass positives of any subject as derived 
from the daily work can best be verified by making a contact print 
on glass from one of the three glass positives. When dry it must 
superpose on all three glass positives. The result is better visible if 
the contact print is converted into a colour print, say a blue Cyan 
print or Uranotype. 

The original negative can be verified by printing a glass positive 
from the reversed negative, and superposing it on the other two 
negatives. These are the proper ways and means of honest verification. 

One of my critics used a toned bromide print and two superposed 
carbon prints, the paper supports stretching different ways, and 
yet blamed the glass negatives for being out of register. 

The colour correctness of the results gives another ground for 
criticism. Here is how it is applied :-— 

One of the great process houses in town had to make a block 
print of one of my views for a publisher, and when the three colours 
were superposed, it represented a completely black smudge; even 
the sky was black, and yet when each negative was printed in the 
ordinary way on P.O.P., all the details and graduations as demanded 
of a good photograph were present as a sure guide for the engraver 
and the photographer. 

I take it that the engraver did not expose his screen negatives 
correctly, or did not etch the copper plate properly, or used a badly 
cleaned roller for rolling up delicate colours. May I be permitted to 
ask, did he know his technique, did he exercise his proper skill, or did 
he do such foolish work for a motive ? I may add he was paid for the 
work. Needless to say the publisher was convinced that the one- 
exposure man was a swindler of the first water. The amenities of 
a specialising worker. 


VERIFYING THE FOCUS 89 


One-exposure camera work should not be difficult for the 
process man to adapt, even if there is no colour picture as a guide, 
because there are, nevertheless, in every three-colour negative certain 
indications recorded, which help to prove that the negatives or posi- 
tives can be read for colour values. High-lights and light subjects 
should surely be rendered as such in the block, and blacks and deep 
shadows give the other extreme; and to my mind colour subjects 
are better rendered if the extreme shadows are weak, than when the 
high-lights are over-printed, but to make a black print with three 
colours is absurd. 


90 COLOUR PHOTOGRAPHY 


CHAPTER XXVIII. 


PROCESS “FAKING 


graduated. The high-lights, reflex lights and whites which 

are exposed directly to white light must show full density 
in the negatives; by full density I mean, just so dense that in a 
P.O.P. printing exposure of ten minutes in good light no appreciable 
discoloration takes place. Further, the most transparent parts in 
the same negative representing the deep shadows and black objects 
should print at the same time to a good black without, what the 
professional calls, turning bronze. 

If we make glass positives from the negatives, either by contact 
printing or by light projection, they should show the exact opposite. 
If we under-expose and over-develop, we stretch the scale of gradua- 
tion and lose some of the middle tints, by merging the latter into the 
high-lights and shadows. If we over-expose and over-develop we 
add extraneous colour values, we alter the area of the deep shadows 
and flatten out the remaining scales of half tints. Thin positives 
favour over-crowded process blocks, dense positives suppress the 
fine middle tints and are the first cause of destroyed colour values. 

The positives can be retouched, in some cases it is even ad- 
visable. A small wash with aniline dye will sufficiently intensify 
certain colour renderings, for example: We take a straw hat, always 
as being yellowish, but actually in the original the colour is a very 
feeble cream and hardly differentiated from white. To gain the 
popular approval a little intensification on the yellow positive record 
would greatly improve the colour. Then there is that gap in the 
green, a wash in the corresponding parts in the red negative record 
or over the yellow positive record would greatly improve the colour 
rendering without destroyjng the half tints. 

When the process man receives the glass positives he has first 
to make screen negatives ; naturally here also a good man can do 
good or negligent work just in accordance with his applied know- 
ledge, skill and understanding of the requirements. 


NU ceases. taken for three-colour work should be well 


PROCESS FAKING OI 


No reversing prism or mirror is necessary when a negative in 
the correct position is to be made from a glass positive, and the 
illumination should be made in the orthodox way by reflected or 
by filtered and dispersed light; the exposure through transparencies 
should never be made by direct arc light, which cuts up all half tints 
and reduces all high-lights to flat fields. Asamethod this is favoured 
by the operator when he is pressed for time. He does not like 
working with glass positives, because he has to alter his camera 
position, and attend to other little things which are not in his daily 
routine. 

When, with the aid of the screen, the continuous half tints of 
the original are transformed photographically into dots, it is perfectly 
easy to expose so, that the dots representing the middle tints are over 
or under-exposed. The negatives can be made so that the dots are 
too much or not sufficiently joined up in the high-lights. The dots 
in any negative can be made larger or smaller, a larger dot meaning 
a darker picture and a smaller dot a lighter picture. 

When the screen negative obtained is printed on the chromated 
metal destined for the block, the process man can make further mis- 
takes in etching too much or not enough. Besides, it is an understood 
thing, that all former mistakes can be rectified by a fine etcher, which 
is often the official title for “‘ faker.” This admirable person is 
really unable to work without a colour original and is specially fond 
of correcting the red plate, and fine homogeneous patches he makes 
of it, faking out all details; parts of these doctored pictures have 
in this way lost their rotundity. 


92 COLOUR PHOTOGRAPHY 


CHAP RE RX 


DIAPOSITIVES 


OR collotype three reversed negatives are required, and for 
| eee a process the plates on which the negatives are obtained 

can be inserted in such a manner that two negatives are taken 
one way on glass plates and the third negative is taken the other way. 
This Jatter is taken on glass or celluloid, but both have to be printed 
through the back. The slight unsharpness introduced when glass 
is used is very small, specially so if printed in direct and not by 
dispersed light. 

It is not advisable to use celluloid for larger plates, as such a 
negative is inclined to deformation, through shrinkage and unequal 
dessication or through hygroscopic influences. 

A new collotype-like process was suggested by Handel Lucas, 
in which bromide prints are treated as in the bromoil method, and 
coloured up with fatty inks in colours. The inventor claimed 
to be able to print a thousand prints from a prepared bromide print 
by means of a resilient transferring pad. This very promising 
process has been killed in its infancy. 

At present it is only three-colour printing from process blocks 
which offers the means for book illustrations, though I am told that 
when the half-tone method is employed in conjunction with the 
offset. press any number of prints of great equality can be taken off. 

If colour record positives are required for block making, then 
paper positives, which are generally called “ prints,” are of ques- 
tionable service. The paper may stretch unequally when it has to 
go through the different photographic processes, so on the whole, 
it is best to supply positives on glass, also called diapositives, to the 
photo-engraver. 

Three-colour negatives taken with the one-exposure camera 
have no grain, when compared with screen colour plates, one-plate 
colour transparencies or Autochromes, and can therefore without 
detriment be enlarged five and more times the original negative size. 

When making glass positives I find the ordinary slow speed 
bromide of silver plate good for the purpose, though I prefer wet 
collodion plates. 


DIAPOSITIVES 93 


Two right-sided and one reversed negative are supplied by the 
one-exposure camera, and we have to redress the reversed negative 
when copying for the above purpose. Certain precautions have 
also to be taken, so that all negatives are placed at the same focussing 
distance in the enlarger or copying apparatus. We have in fact to 
account for a difference of a glass thickness. The three negatives 
should be on glass of the same thickness and the copying must be 
done in conjunction with a plain glass of the same thickness in such 
a manner that the gelatine film holding the photographic negative is 





Fig. 39.—Adjustable exposure frame. 


always sandwiched between two glasses ; then the focal length is the 
same for all, which enables us to give the copying camera a fixed 
focus for all three exposures. 

If one negative of the set of three is on a celluloid film, the best 
plan is to make contact positives. It is also advisable to use glass 
of the same thickness for the positives, in which case we can make 
the enlarged negative from the glass or film side of the positive. 

The different negatives and positives should always be spotted 
before they are used for the next process. 

When making glass positives or negatives from transparencies 
an “‘ adjustable exposure frame ” (Fig. 39) seems to be necessary. 


94 COLOUR PHOTOGRAPHY 


COAP PE Rex 
_THE GREY PRINTING Pia 


HEN the painter has laid down the outlines of a painting 
\ \ he will, if using fairly transparent colours, fill in the shadows 
and darker half tints with grey before colouring up, and 
later to enhance the pure blue, green, yellow, orange and red he is 
sure to work over the half tints with a darker colour. The deeper 
the half tints the darker will he use the colour ; and he has no scruples 
in using grey or black to set off the colours. Such method has the 
effect of making the colour where pure to appear much more brilliant, 
but with all the addition of grey and black the painter husbands the 
colours; he does not mix black and grey with blue, green, yellow, 
orange or red where such tints should be pure; such admixture in 
his opinion would degrade the colours and produce only night 
effects. | 
When the three-colour half-tone process came into use, the 
want of a grey plate was soon felt and the photographic expert 
thought that when taking a fourth negative through a yellow filter 
he would have the necessary correction or colour balance for grey. 
Some more economically inclined thought the blue filter negative 
could be used for the two purposes, wz.: a yellow printer and a 
grey printer. Others thought the blue or red record negative 
better for the purpose of making the fourth screen negative from. 
This would answer if the required positive was made, so that the 
half tints merged into the high-lights, obtaining a sort of skeleton 
reproduction allowing only the most transparent part to form the 
screen negative. Supposing now this skeleton plate, obtained from 
the yellow printing negative is printed in grey or black, and the 
yellow print from the proper yellow printing plate is superposed ; 
does this combination further a good colour rendering ? The expert 
says it does. For my part I do not believe it; if I mix black and yellow 
together on a palette nobody would take the mixture as an improved 
yellow. Why should it, if it is done in two operations by way of 
printing ? 
A certain house took up carbon printing for the purpose of 
making portraits in colours and thought to evolve a process of its 


THE GREY PRINTING PLATE 95 


own. To that end the fairly permanent yellow was discarded and 
substituted by a bromide print toned yellow with Farmer’s mercury 
iodide intensifier, to which no hypo had been added. This com- 
pound was not stable, any alkali in liquid or gas form bleached the 
same, and so did the daylight. But to bring us to the point we 
discuss, it was claimed that if the bromide print was not completely 
converted into the yellow state, the remaining and unconverted grey 
silver compound would form a grey key, that is the fourth plate. 
This is in no way the case, and the idea is the outcome of want of 
knowledge of the requirements. The fact is, if your plate or print 
is not fully developed (in this case for the yellow) a flat and smudgy 
result is the outcome; and also yellow with an admixture of grey 
is not a pure or brilliant colour. 

In a one-exposure camera we have always one reversed negative 
and as a rule it is the red printing record. In a red filter negative 
the parts representing yellow to deep orange are covered, allowing 
all blue to be printed, and in a blue filter negative, blue-violet, blue 
and green is fully exposed allowing all yellow and orange to pass and 
therefore to be printed. If now we superpose these two negatives, 
film to film, in exact register, practically all the pure colour values 
in this compound negative—the colours which the printer tries to 
keep pure—become opaque and only the fully transparent and also 
some half tints remain in such a condition as to allow a good positive 
to be taken therefrom; shorter or longer exposure will give all 
variation one can require. It seems to me that such a positive if 
used as a basis for the fourth plate is a much more satisfactory medium 
for printing the grey, as it leaves all places where pure colours should 
be shown quite free of any admixture. 3 

The taking of direct screen or half-tone negatives for colour 
work, has been abandoned in some houses, and the screen nega- 
tives are made from glass positives, of which the colour. negatives 
taken direct are the origin. If these colour negatives are always 
taken with another glass, film side between the two glasses, and if 
the reproduction for glass positives is done the same way, then there 
is no chance of bringing in unequal focal length. Therefore there is 
no reason why the red negative could not be taken the reversed way, 
and this system of obtaining the grey printing plate adopted. To 
my mind this system is better than any other and requires little 
or no faking, called fine etching, to bring out the colours in the 
combination print. 


96 COLOUR PHOTOGRAPHY 


CHAPTER] XXX 


LANTERN SLIDES IN COLOUR 


r ; “XO make colour lantern slides, three part positives in colour 
are required, namely, one in blue, one in yellow and one in 
pink. These colours are supposed to correspond to certain 

sections of the spectrum. I have, however, used a pink of which 

I was unable to find the corresponding shade in the spectrum, and 

curiously that pink gave me better and truer results than a red, 

supposed to correspond to a spectrum shade. 

I found that a fair variation as to shade for all three colours, 
least, however, as to the yellow, was permissible. I have used many 
different reds, from orange red to magenta, rose and bluish pink, 
and I obtained therewith fair representations of the object in colours. 

If the yellow employed has the slightest admixture of orange, 
the harmonious colouring is destroyed, but the blue allows all the 
varieties that Turnbull’s blue can assume, without ‘unduly inter- 
fering with a fair colour rendering. These remarks are specially 
applicable to the aniline dyes as for transparencies, where it is easily 
possible to adjust each colour section to the two others. 

As the blue basis of our slide we can use a blue-toned bromide 
of silver positive, toned as described in the following chapter. The 
colour is very good and closely resembles the shade pronounced by 
the expert as greenish blue, whilst it is permanent when having an 
acid reaction. 

The yellow part positive can be printed on a separate gelatinized 
celluloid film or can be printed direct into the very gelatine film 
which holds the blue iron print itself, and to be able to do so, the 
gelatine has to be sensitized with a chromate, free of alkalis. 

This superposition of two prints on one gelatine film as here 
described would have been patentable, but I refrained from filing 
a patent, because my experience has taught me that there is nothing 
to be gained thereby. 

The gelatine film has to be sensitized, and one way of doing 
this is to use a large flat brush and gently apply for about one minute 
a six per cent. solution of ammonium bichromate, to each 20 ccs. of 
which has been added a drop of sulphuric acid. 


LANTERN SLIDES IN COLOUR 97 


Another way of sensitizing is to immerse the gelatine film for 
two minutes in the following solution : 


Ammonium bichromate 6% ROECCS. 
PeeesOULICs e..- .. - 50% 12 drops. 
Duetemmorcdinary... .. -.. ..-- 60 CCS, 


It is advisable in both the above cases to pass the plate thus 
prepared quickly through some clean water to eliminate the surplus 
sensitizing solution, before putting the plate up to dry. 

The dry chrome-sensitized blue-toned positive is put into register 
with the yellow printing negative record, or the plain sensitized film 
is printed in the orthodox way, and the printing is done in the direct 
sunlight. 

For a medium strong negative the exposure is about ten minutes. 
When printed the chrome positive is then ready to be washed free 
of soluble chrome salts before it is coloured up. 

For the red part print, a reversed negative, such as the one- 
exposure camera gives, is of great utility, as then the cover glass can 
be gelatine-coated, and also chrome-sensitized ; if, however, all the 
negative colour records are same sided, then the red should be 
printed on a gelatine-coated celluloid film, or the negative can be 
printed through the back on to the cover glass, when naturally some 
unsharpness will be introduced. 

To obtain a gelatine-coated film or plate, ordinary dry plates 
can be fixed out, well washed, dried and then chrome-sensitized, or 
it is also possible to coat plates, either with plain gelatine or with a 
warm and filtered chrome-solution of the following composition :— 


Gelatine, Coignet’s photographic .. .. 18 grms. 
Water,,ordinary <. .. ge See ZO ECCS: 
Ammonium Paul, 6% iia ie TOsccs. 
Polgesuonuric, 507, stock ..  .. .. §20 drops. 


This is sufficient to coat fifty quarter-plates. The plates before 
coating are properly cleaned and dusted, warmed and placed on a 
level slab. By means of a measuring spoon the solution is poured 
on the centre of the plate and the flow is assisted by the same utensil. 
When the coating has become properly set the plates are stood up 
on a drying rack and slightly heated air may be used to dry the plates 
quickly ; not more than ten hours should be allowed for that pur- 
pose. If, however, the plates are overheated, the bichromate will be 
decomposed to a lower chromate, and when printed will show 


98 COLOUR PHOTOGRAPHY 


bluish on white, whereas if correct the print shows a good brown or 
very light brown, which colour will not completely disappear, when 
the plate is freed of the soluble chrome salt by washing. The faint 
colour remaining is of no consequence, but could be eliminated with 
a weak solution of sulphuric acid, partly to the detriment of the 
positive. 

The colouring of the chrome prints is done with aniline dyes 
and they have to be fast and acid-proof; for this purpose acid 
yellow and acid red are used. If acid added to a dye solution de- 
composes the colours or changes the shade of them then they must be 
rejected. The strength of the colour solution is about five grammes 
of colour to a litre of water, and it is acidulated with twenty drops 
of acetic acid. 

If the colouring is done in neutral or alkaline solutions the same 
will be very irregular and in some cases no proper colouring takes 
place, nor can proper transparent whites be obtained afterwards, 
the gelatine remaining stained in all parts. This is especially notice- 
able with the red prints. 

The chromated plates are printed till the picture is well seen 
in a brownish colour; they are then removed from the printing 
frame, well washed for about half an hour in frequent changes of 
water. Washing in running water is not to be recommended, as it 
tends to very irregular washing out of the chromates and through 
that to irregular colouring. When washed out for sufficient time, 
the plates are immersed in the respective colouring solutions for 
twenty to thirty minutes, so that they become coloured through and 
through. If the plates when coloured show a slight positive, or 
show no picture at all, they are in the best of condition; if they 
attain only to a negative the time of soaking in the colour-solution 
should be doubled. 

Freshly made colouring solution is recommended ; it can, how- 
ever, be used twice or three times in the course of a week or two. 
If sufficiently coloured the plates are then washed in repeated changes 
of water, when the pictures will gradually become clear colour 
positives. Theless exposed or less hardened parts release the colour 
quicker than the well exposed and more insoluble parts of the gela- 
tine. The coloured plates can be stored before washing out any 
of the colour, or may be partly washed out and the complete washing 
out can be done at any time. This washing out of the colours may 
take up to one hour with the yellow and up to several hours with 


LANTERN SLIDES IN COLOUR 99 


the reds. With the reds a few drops of ammonia can be added in 
the last waters; it helps to clear the high-lights; but ammonia 
must not be used with the yellow when blue and yellow are in one 
gelatine film, because ammonia in small quantities will give a violet 
colouring to the blue, or in slightly larger quantities will dissolve 
the blue, because Turnbull’s blue is soluble in all alkalis. 

Practically any acid added to the last washing water will keep 
the blue in good colour and also will fix the colours sufficiently. 

' When a certain experience has been gained one is able to 
judge with fair correctness how far the positives have to be cleared 
of the superfluous colours. When the latter point is reached, to 
prevent markings and irregularities, the water has to be mopped off, 
with a soft cloth or blotting paper, and the plates have then to be 
dried. When dry the blue, yellow and red positives are superposed 
and the artistic test will tell which-colour has still further to be reduced 
by a renewed washing out. It is this balancing and adjusting of 
the colours which is a great advantage. 

I have tried to apply the same process, to making prints which 
are viewed by reflected light. Blue and yellow on an opal glass do 
very well, but on a paper the yellow cannot be properly washed out 
of the whites. Some ingredient of the paper composition acts as a 
mordant and takes up the colour as a fixed dye. There is also a 
drawback with the red stained positive when printed on a glass, and 
in that state superposed on the blue yellow combination, because it 
will always reflect predominantly the top colour. 

For this process I have also tried to make a stripping gelatine 
film on a collodion basis, but the latter also takes up the colour as 
a fast dye, preventing thereby clean and clear whites in the high- 
lights. A further disadvantage is that the two insoluble surfaces 
refuse to properly adhere to each other with best glue; the top 
picture will peel off, the surfaces being evidently too glossy. 

I indicated that in the last stage of washing out the red colour 
a little ammonia could be added to the wash water as a help to clearer 
high-lights, and this addition does not affect the sharpness of the 
colour positive ; I think it rather helps to accentuate the sharpness. 
This is, however, not the case when adding soda carbonate or similar 
alkalis ; the colours seem to spread out or run, similarly to a drop 
of colour on blotting paper. Dr. Jumeaux is the originator of this 
process. 


100 COLOUR PHOTOGRAPHY 


CHAPTER XXXip 


BLUE TONING 


bromides are often required, but the different processes 
known at present for toning a bromide image blue, ive, as 
far as I have tried, no satisfactory and regular results. 

When using a direct toning process, that is, toning at one 
operation, we find that the image is intensified in a manner not very 
controllable, and is too often blue over-toned to the detriment of 
the finer details. If we take twelve pictures and tone them one after 
the other, we obtain twelve pictures differently shaded in blue. 
The first toned picture has a colour resembling indigo with probably 
clear whites, the last toned picture has a milky blue appearance and 
there is no white where white should be pure and clear; it looks 
as if the gelatine had also been toned, as well as the picture. 

With the process known as the indirect toning process, first 
bleaching and conversion into blue after, I also obtained nothing 
very satisfactory. It did not much matter if the solution was acid, 
neutral or ammoniacal. 

After experimenting for a long time and in different directions 
I thought that the red prussiate alone did not convert the bromide of 
silver into such a state as to be easily converted into blue, and I 
looked out for chemicals assisting a better bleaching. At last I 
found a process which gave me absolutely sure results either for 
glass positives or paper positives and, moreover, in such a blue as 
is required for the blue part print in colour photography. 

The bromide positive is bleached in the following solution :— 


Pe= colour transparencies and other processes, blue toned 


A. Freshly made red prussiate solution 3°% 100 ccs. 


Soda carbonate stock 10% ae ss TOgss 
Ammonium nitrate stock 10%.. a 10, 
Chloride of sodium 10° < = 10s 


If we change the soda carbonate for ammonia the conversion 
to a blue picture will be weaker and the tone will be more blue 
violet or ultramarine. 


BLUE TONING IOI 


The above bleaching solution decomposes slowly, but will 
act well for about half an hour, and the given quantity will be suffi- 
cient to bleach about twenty-four half-plates. The grey black of 
the bromide of silver will not be bleached out to a white, but will 
be converted into a picture having a light grey-brown appearance. 

Before immersion in the bleaching solution, the dry positive 
should be moistened for a few seconds in ordinary water. This 
will help to equalize and regulate the action of the chemicals. 

The bleached picture, after being well washed, is converted 
into a blue in the following solution. 


B_ Potass. bromide stock 5%, 10 ccs. 
Acetic acid stock 10% Loves 
Iron alum stock 3%, AC ame 


I generally use ammonium iron alum. This solution B de- 
composes fairly quickly, and is only sufficient for about twelve 
half-plates. The acetic acid can be replaced by one per cent. hydro- 
chloric acid, but the toning solution is thereby more quickly de- 
composed. When the pictures have attained a milk blue or steel 
blue appearance then the toning is complete; to tone longer is not 
injurious nor will the tone be changed. After the toned positives 
have been properly washed, they are again fixed out for five minutes 
in a five per cent. solution (preferably acid) hypo and after a good 
washing they are cleared in a one per cent. solution of sulphuric 
acid for about two minutes, which must be followed by a last short 
washing before the positives are placed on the drying board. 

When using the above toning process, the original positives 
have to be developed to full strength, because there is no intensifica- 
tion by this process; if anything they will be slightly lighter. The 
white parts will be absolutely clear and not over-toned in any way. 
The gelatine is not affected nor has it any influence on the results 
if the positive remains a little longer in one or the other solution. 

A further advantage is that toning by two operations does not 
tone or colour the fingers at the same time, and the vessels employed 
will also remain clean and clear, for the simple reason that the solu- 
tions form no incrusting or precipitating sediments. 

If the bromide of silver positive is found to be too dark, it can 
easily be made lighter without sacrificing the half-tones by immersing 
in a hypo bath to which has been added some red prussiate and a 
small dose of soda carbonate. The latter addition imparts a quick 


102 COLOUR PHOTOGRAPHY 


and equal action, so it is advisable to make the reducing solution 
not too concentrated. 

Like all other bromide of silver prints converted into yellow 
and red, the blue toned one, if too strong, can be reduced by an 
alkali treatment. A week ammonia solution will attack the high- 
light more than the deeper coloured parts, whereas a weak carbonate 
of soda solution will act just the reverse way, and the prints by the 
latter treatment seem to lose in sharpness. If the alkali acts too 
long the print may entirely disappear. After the few seconds 
necessary to reduce the toned colour print, it is washed and fixed 
in a half per cent. solution of hydrochloric acid. However, prints 
treated in this way do not seem to be so permanent as the undoctored 
ones. 


CARBON PRINTING 103 


Sri EL ERO SITE. 


CARBON PRINTING 


\HE colours which can be used as pigments in the carbon 
process are very limited. We have only an insoluble violet- 
3 blue, not a green-blue as required; for the yellow we have 
only metallic oxides which are in no way transparent ; and for red 
only the madder red of organic derivation. It is also possible to 
use alizarine as an aniline lac, and as such is liable to make the 
gelatine irregularly soluble, like all lacs do. The reds have an 
orange tint, they are not pure pinks. The printer using fatty inks 
has a better colour range at his disposal; solubility in water does 
not hinder him in using such colours. 

The carbon pigment papers, also called carbon tissues, on the 
market are anything but colour correct, or even uniform in working. 
If prints are made from one negative only, say one print in blue, 
another in yellow, and a third in red, we find the developed blue 
print hard, the red too flat and the yellow right, if all the tissues are 
treated alike throughout. 

For our purpose, however, the blue print should be flat and 
very thin, because blue has the greatest covering power in combina- 
tion with the other pigments; for the red print more contrast is 
desirable, because the red has distinctly less covering power in the 
stronger portions than in the thinner and more delicate parts of a 
print. These phenomena will give the clue as to why a thinner 
negative is preferable for a blue record, and shows that a contrasty 
negative should be employed to print the red from. A strong 
negative is also required for yellow, because no transparent yellow 
exists fit for such printing, and on account of this opacity the yellow 
is used to form the first print near the paper. A fuller initial con- 
trast is a necessity to bring the yellow to effective account so as to 
shine through the other two more transparent colour superpositions. 
The yellow is therefore subject most to the influence of the ground- 
glass variety, as explained before in an illustrative way. 

Suitable for our purpose we find three-colour pigment stripping 
films on celluloid on the market, and also carbon tissues on paper 
supports, the latter are much cheaper and give much sharper 


104 COLOUR PHOTOGRAPHY 


pictures, because the former have to be exposed through the film 
thickness, and the latter are exposed direct on the tissue. 

The manipulator who develops a carbon tissue on a collodion 
film, or on an india-rubber coating, supported on glass, has the 
advantage of being able to use water of any temperature, enabling 
him to clear the print perfectly of any superfluous matter; he has 
not to be afraid of cockling his support or losing it in the developing . 
solution, and if he has once used the glass support he will find it 
to his advantage to always adopt it. 

When printing with the sensitized carbon paper, we have to 
print the yellow tissue till the image is visible as a brown-orange 
impression on the yellow surface ; we can thereby very easily judge 
the depth of printing. The print on the yellow tissue can therefore 
be made use of as an exposure meter, because the other two tissues 
show no such change when exposed. If the yellow print takes fifteen 
minutes for full exposure, then the red would take about twelve 
minutes and the blue six to seven minutes in case all negatives are 
of the same density. The correct shading of the blue is the most 
difficult to attain and it is on that account ada to print the 
blue in duplicate. 

The blue printing is the difficult one, as I have said before, 
because blue possesses greater covering power and also because the 
blue pigment does not absorb the light actinity, like the other carbons. 

To counteract this as much as possible and to reduce the pene- 
trating action of the light, as well as to prevent the formation of a 
deep relief, I have tried to add soluble yellow colour, forming quasi 
a stronger yellow light filter than the chromate can form. By ex- 
periment I have found that such addition is best made by adding 
the water-soluble colouring matter to the sensitizing bath. This 
addition to the blue tissue I found of great advantage, but of no 
influence on the yellow or red tissues, which allow us to use a 
uniform sensitizing bath for all tissues. 

The sensitizer for carbon tissues I recommend as follows :— 

A. 10 grammes of potassium bichromate dissolved in 250 ccs. 
of water, neutralized with ammonia till the orange colour 
has changed to yellow. 

B. 10 grammes of potassium bichromate in 250 ccs. of water 
and when dissolved add two grammes of tartrazine or any 
other similar colour that is not thrown out by the chromate. 

A and B are mixed, and used only once when cold. 


CARBON PRINTING 105 


Enough solution should be poured into a dish to facilitate a 
proper floating of the tissue. Immerse the same for two minutes, 
giving the proper attention to turning it over and of moving 
the solution to facilitate an equal sensitizing; then remove from 
the solution, pass the tissue through clean water for a second or two, 
place it face down on a clean slab or glass. Remove with a squeegee 
all fluid, and then wash or rather mop the back of the tissue with a 
sponge to remove superfluous sensitizer and all running liquid so 
as to facilitate drying, finally hanging up the tissue to dry ready to 
be used next day. 

I do not recommend storing it in calcium tubes, because a small 
amount of moisture in the tissue is necessary ; absolutely dry tissue 
is too brittle and does not print properly. It is naturally possible 
to use older tissues, but if regular work is valued and desired, and 
as it depends on equal sensitiveness of the tissue, then put up with 
one rule and stick to it. 

In warm weather, when sensitizing, put your dish holding the 
sensitizing solution into a larger dish and allow the tap water to pass 
into the larger dish, thus keeping your temperature below 16° C, 
(60° Fahr.) 

In calculating the exposure necessary for carbon tissues, I find 
a Bee-meter also very useful; the time of darkening the dark tint 
multiplied by fifteen during mid-day is near the mark, as required 
for the yellow tissue. é 


106 COLOUR PHOTOGRAPHY 


CHAPTER Xo. xe 


CARBON TRANSFER 


one red), we have to develop them and for this purpose I re- 
commend the collodion transfer process. 

Select the glass to support your prints of such quality that it,is 
free from specks and let it be larger than the print to be mounted on 
it. Wash the glasses well and polish the best side up. Charge a 
cotton tuft with dry French chalk (“ talc ’?) and apply it with gentle 
friction to the clean surface, dust, border the plate about a quarter- 
inch wide with a thin solution of india-rubber, to destroy the slippery 
surface and give to the collodion an edge for firmly attaching itself 
to. On the surface not prepared, stick a small paper mark to pre- 
vent any mistakes. 

The india-rubber solution is prepared by dissolving a little 
pure rubber (not vulcanized rubber) in chloroform, and the perfectly 
liquid solution is applied with a small soft brush by passing once 
round the border of the plate. 

Collodionize the prepared plate surface with a three per cent. 
enamel collodion, and when the collodion has set, immerse in water 
till all greasiness has disappeared before surfacing with the carbon 
tissue. I recommend large tanks with grooves, so that a number of 
plates, say one day’s requirement, can be prepared and kept in the 
water. All collodionized surfaces should be turned to the left side, 
the side of the thumb, and the tank should be marked accordingly. 
Preparing the plates in such a way in advance has no deleterious 
effect on them, and we have in this way the vaporized solvents only 
once in the house during the day. 

I once prepared collodion plates, stored them dry, and soaked 
them in water before use, but I found that the collodion film gets 
too horny, and the gelatine film does not enter into homogeneous 
contact, which is shown by the air bubbles formed between the two 
films, and these are multiplied by the following application of a 
squeegee. | 


|: we have printed the four carbon tissues (two blues, one yellow, 


CARBON TRANSFER 107 


Have your collodionized plates ready to hand, then prepare a 
dish with cold water, not over 18°C. (64° Fahr.). Immerse one 
carbon print in it, turning it over to eliminate all air-bells from the 
surface of the tissue, take note of the time it requires to get flat, 
which will be about sixty to ninety seconds, then, without losing a 
second, lay the tissue, film down, on a wet collodionized plate, cover 
with a protecting cloth and pass your large squeegee with one firm 
stroke over the lot, which should give proper adherence to, and 
eliminate all superfluous water and possible air-bells from between 
the two films. Then with the aid of blotting paper mop up all 
- moisture from the back of the tissue and let it stand for ten minutes. 
In the meantime, the same operation has to be performed with the 
other tissues. Be sure that the time of immersion is exactly the same, 
because that is the condition for securing equally expanded films. 

After having allowed ten minutes for each mounted tissue to 
dry, ensuring proper adhesion, soak it again in cold water, not less 
than five minutes, but not more than two hours before developing 
in warm water, see also that no air-bells are formed outside when 
putting it in the cold water again. 

Before starting to develop, have a fair amount of warm water 
ready, so that you can afford two or three changes of water for the 
express purpose of ridding your carbon film of all chemicals and 
soluble colouring materials. When ready to develop, immerse 
your glass holding the print in water of about 40 to 45°C. (104 to 
113° Fahr.), and when the known characteristics show that the 
paper can be removed, do so with a steady pull without rubbing the 
tender film on the collodion and take equal care in clearing the 
print. Warmer water can be used if necessary, but do not use 
force or work with undue haste to clear the prints; the penalty is 
irregular and hard prints. Remember that these colour tissues do 
not dissolve so quickly as ordinary gelatine. 

The appearance of the print should be delicate and of about 
half the strength required for an ordinary one-colour print; if too 
strong then an addition of a few drops of ammonia to the developing 
water may remedy the defect a little. When sufficiently developed 
rinse in cold water and stand up to dry. 

Instead of collodionized plates, india-rubber coated plates can 
be employed, the rubber solution being of the consistency of treacle. 
When the solvents have evaporated, the plate is ready to hold the 
tissue. 


108 COLOUR PHOTOGRAPHY 


The text books say that sensitized carbon tissue in a wet state 
is no longer influenced by daylight. This is a fallacy; what is true, 
however, is that the sensibility to light has been reduced to half or 
one-third. The deleterious effect of exposure to daylight even 
during development is very quickly noticeable, when the three prints 
are superposed, therefore keep the wet carbon print, as long as it 
contains the slightest trace of chromate and as long as the same is 
not fully developed, guarded from daylight or actinic light. 

The three part prints have to be dry before they are ready for 
superposition, and for that purpose we require a solution of glue. 
Best light-coloured transparent glue about 20 grammes is dissolved 
in 500 ccs. water. If the solution when cold keeps liquid, then our 
mounting solution would not act properly. I say this because by 
introducing wet part-prints and wet collodionized plates we con- 
stantly add diluting material to the glue and if we desire to use the 
glue solution from day to day, we must keep it up to the required 
strength. The other extreme is a glue of stronger percentage than 
is required, because it would set too quickly and thereby prevent 
an easy superposition of the prints. 

The paper on which the three part-prints are superposed should 
be of good quality and hand-made paper is very good. Sawyer’s 
Temporary Support (No. 112) if used on the side not prepared is 
acceptable. I have made experiments in the direction of non- 
stretching paper and I think the following is perfection. Take 
the best quality glazed baryta paper and collodionize each side, 
use when dry. The paper prepared in such a manner does not 
stretch and has an unchanging white of the most approved quality. 

When ready with the preparations, warm the glue to about 
50°C. (122° Fahr.) filter through fine muslin into a dish, which should 
be kept warm by some means. Immerse the glass print in the warm 
glue solution for two minutes, so that the glue is properly soaked 
into the print and the glass itself becomes warm. The water-soaked 
paper is then also passed through the glue solution, paper and glass 
print are superposed, the squeegee is applied, but only so that all 
superfluous matter and all air-bells are eliminated. There must 
be enough glue left to fill up the paper pores or any amount of air- 
bells will appear when the transfer is complete, showing thereby 
that only part adhesion between the two exists. It is the yellow 
print that has first to be mounted, and when the operation has been 
performed, mop up, with the aid of a sponge dipped in warm water, 


CARBON TRANSFER 109 


all superfluous matter, then stand up to dry in an even and not 
forced temperature for about twenty-four hours. When this 
yellow transfer is dry, cut through the collodion film at the border 
of the paper and lift the print off the glass. If the print does not 
detach easily and properly, it would be an indication that the print 
is not thoroughly dry or that the talc has not filled up the glass- 
pores. The other two part-prints are mounted in a similar way, 
leaving the most transparent for the surface print. 

In mounting the second print, immerse the print again in warm 
glue solution, and also the yellow print, which latter should have 
been soaked in a five per cent. formalin bath for ten minures and 
well washed before putting it in the glue solution. The two are 
taken out together, squeegeed, and with a warm sponge and warm 
water the plate is cleared; it should also be kept warm so that the 
final adjustment of the two prints can be done before the glue sets. 
When the two prints are in perfect registration allow the glue time 
to set firm, before the prints are finally cleared of the superfluous 
glue. When dry and detached from the glass support the third 
print is mounted in a similar way. 

A preliminary superposition of the three part-pictures when 
still on glass can be made, and to prevent damaging the delicate 
picture film, paper wedges between and at the corner of the glass 
must be inserted, but no accurate judgment or anything near it 
can be gained. The internal reflections, in the glass and also the 
dimness of the pigment film gives it the appearance of irregularly 
coloured ground glass, thereby preventing correct judgment even 
when superposed on white paper. 

When the composite print after the third superposition is dry, 
and detached from the glass, keep under pressure for a time, so that it is 
made to lie flat. The picture will be glossy when taken off the glass 
in a dry state. For an experienced man it would be possible to take 
the last print off the glass directly after the glue has set, when the 
print will be matt. 

The retouching and spotting of this three-colour print is not 


very easy, but if prepared oxgall is used with prussian blue, cadmium 


yellow, and alizarine water colours, small defects may be remedied. 
It should be remembered that an orange-red spot is to be subdued 
with the complementary or missing colour blue, yellow with blue- 
pink, blue with orange, and green with pink. 


110 COLOUR PHOTOGRAPHY 


CHAPTER XXog\s 


CINEMATOGRAPHY IN COLOURS 


producing the first result in Cinema work with two colours, 
have asked me for an article on this subject to be included 
in this book. 

The two methods of colour photography have also impressed 
themselves as a natural consequence of the existing knowledge in 
colour photography, in the moving illustrations of daily life. 

Mills, I think, is the only one who had some success with the 
subtractive method of colour photography. His results, which were 
fairly good, were shown in private about 1914-15; the subjects 
shown were very slow-moving or nearly stationary subjects. 
The printing of three different colour films in superposition was a 
long affair, and very likely the commercialization fell through on 
that account. 

Up to the present the semi-additive methods have shown no 
results, because, when enlarged on the screen, the grain or the 
separate particles of the three-colour basis became too discernible 
to the eye. They can no longer amalgamate in a harmonious and 
homogeneous unity ; also it is not possible to multiply the one film 
for the service of the million. 

The main and principal direction in which cinema in colours 
can be made of use is, to my mind, by the addition method pure 
and simple. 

Colour cinematography by the addition method was inaugurated 
by Lee and Turner, Pat. 6202/1899, at their St. Ann’s Well Studio, 
Brighton, but no results seem to have been obtained, mainly through 
want of a good colour sensitizer. Azalin was not rapid enough. 
Orthochrom T. was discovered about 1902, and Pinachrom a year 
or two later. 

The first result in cinematography with two colours was obtained 
by Davidson and Jumeaux on a small glass plate cinema camera in 
1902, but the patent embodying the invention No. 3729/1903 (see 
Fig. 8, Exterior Prism position, Page 18), was worked on an 


Mi: publishers hearing that I am a worker who assisted in 


‘uaa13-an[q ul pr9afoid aq OL 


CINEMATOGRAPHY IN COLOURS III 


ordinary cinematograph camera; two pictures side by side (see 
Fig. 40). The light filters were stationary, therefore the exposure 
was simultaneous. 

The exterior prism position first suggested by Dr. Jumeaux 
was the formation used by N. W. Lascelles Davidson in producing 
his cinematographic pictures in two colours. 
The results were first shown to the Photo- 
graphic Society in Paris, 1st May, 1904, and 
later at the Brighton Hippodrome, Nov., 1904. 

This process of obtaining two pictures by 
the aid of two prisms and one lens, was later 
followed by Albert Smith’s process, 26671/- 
1906, exposing one picture after another, also 
alternating the light filters for each exposure. 
The different light filters were placed on the 
moving shutter. 

Both systems gave colour pictures tainted 
by colour fringes. The defect in the first 
process is explained in Chapter VII., as 
derived from the prisms. The defect in the 
second is really obvious, irregularity caused by 
two exposures, which the persistence of vision 
was not able to assimilate. 

It is of absolute necessity that the colour 
selection and therefore the exposures for two 
or three part colour record negatives or 
positives, must be simultaneous. 

Instead of using light filters on the camera 
shutter some inventors have thought to cir- 
cumvent Smith’s patent by joining up the 
filters on an endless or circular band and pass 
them during the exposure in front of the 

Fig. 40. sensitive film, and it was also proposed to 

colour the positive film to save using the light 

filters; the colour fringes were not removed, seeing that the 
exposures were not simultaneous. 

It has now been proved that a slight stereoscopic difference, 
where the lenses are placed vertically instead of horizontally, does 
not show as a whole the colour fringes to a noticeable extent. Nearly 
everything in Nature moves in a horizontal direction—the man, the 


To be projected in Orange. 





II2 COLOUR PHOTOGRAPHY 


vehicle, the train, the wind, etc.—and the movement in a vertical 
direction is really very small. 

The first indication for such a purpose and the possibilities of 
such a battery of lenses is given in the English patent 25908/1906. 

The peripheries of the lenses where they join are cut away to 
bring the lenses more together, making effective use of the optical 
centres, and to shorten the picture distances; also to reduce the 
stereoscopic differences to a minimum. 

The English optical trade would not countenance such an 
absurd notion, but it was taken up by Gaumont, Paris, after the 
English patent had elapsed, and the invention was embodied in some 
mechanical means as shown in patent 3220/1912. Some unsur- 
passable results were shown in that year at the London Coliseum. 

It is obvious that special machines, cameras, projector, etc., had 
to be made for such work and what is more it will never be possible 
to do without such means. 

A specific work requires a specific treatment, with specific 
machinery, and yet to-day the wiseacres of the English cinema 
trade ask for new ideas in two or three colour projection on the basis 
of the old existing machinery as used for mono-colours. 

These cinema colour processes here mentioned are the only 
ones that have been used, at any rate I am not cognisant of others. 
It is true there are old and new patents galore on the subject, and 
they are still forthcoming. My description on the optical means 
in which reflection and refraction are spoken of state some critical 
points, and most likely may point to the inherent troubles of the 
new systems proposed. I find the cinema trade full of optical 
conundrums. 


KINO-STEREOSCOPY II3 


CHAPTER XXXVI. 


KINO-STEREOSCOPY. 


INCE the earliest days of the kinematograph industry, innumer- 
Se: attempts have been made to produce stereoscopic motion 

pictures, yet no really practical method has been suggested 
so far. One might be getting pretty near the solution of this state 
of affairs in saying, that the fundamental laws governing stereoscopy 
have not been fully understood, and that it has been forgotten that 
the two eyes have to see two slightly different pictures. 





Fig. 41.—Stereo-Conundrum. 


Let us turn to Fig. 41, where “‘ O1 ” and “ O2” are two lights or 
optical centres. It will be seen that two light-cones are projected 
towards a ball ‘‘ P,”’ and also that the light and shadow of the 
combination is thrown on the focussing plane ‘“‘ F.”’ As stereoscopic 
pictures the two images should be a—b and c—d, but we see only 
c—b, for the rest has melted away. If now a positive is 
printed from the negative so obtained, and is viewed with 
two eyes, shall we see a_ stereoscopic representation of that 
ball? Of course not. Yet many an inventor has said 
he does, and has based patent after patent on that impossi- 
bility. So far as the negative is concerned, where two shadows meet 
we have transparency, and where one light-cone passes over the 
shadow of the other, no transparency will be obtained; nothing 


II4 COLOUR PHOTOGRAPHY 


but one deformed composite picture, flat and without any stereoscopic 
properties. Such a picture is worse than would be obtained with 
one lens only. 











t 
, Ox \" O2 | 
: S. 2 “'G ie 


: 
MS EE Bek RS Mi 





Fig. 42.—-Kino-Stereoscopic Taking Device. 


For the purpose of taking stereoscopic pictures a ‘‘ Kino- 
Stereoscopic Taking Device”? (Fig. 42) has to be employed. In this 
two lenses placed at the eyes’ distance apart—that is, 3 to 34 in.— 
form two light-cones at the focussing plane F1 and F2, when two 
separate pictures are impinged on the photographic film. Each 
light-cone is twice reflected, at “M1” and “‘ M2,” to form a narrowed 
down picture in the small focal plane. The reflector “‘ Mr” is best 
formed by a right-angle prism, a—b—d ; ““M2” can be part of a right- 
angle prism “‘P,” preferably made of black glass, or a right-angle prism 
c—e—g with a silvered surface. ‘“‘ M2” can be a part of a—c— 
e—d a form of solid reflecting prism, or an air prism. Additional 
enlarging or reducing lenses (S or L) can be inserted anywhere in 





Fig. 43.—Sight Transposing Prism. 


the light-cone. With such a device we obtain two negative pictures 
side by side, somewhat dissimilar, but of the identical view in general. 
The size, however, is somewhat restricted. 

After having obtained the negatives, as explained above, posi- 
tives have to be printed therefrom, and when placed in a contrivance 
suitable for viewing them, the combined pictures will show in relief, 
that is stereoscopically. For such a purpose a “‘ Sight-Transposing- 


KINO-STEREOSCOPY | IIs 


Prism” (Fig. 43) comes into play. Such a prism obviates the separa- 
ting of the film and transposing the same in printing. The light-ray 
**C” enters the first refracting surface “‘ Rr,” and is deviated from the 
straight course to the second surface “ R2,’’ where the same ray is 
reflected to ‘““R3,”’ and is there a second time refracted at the offside of 
**R3.” The prism has at ““B” an angle of about 76 deg., and to prevent 
the possible overlapping of the picture a partition ““H”’ can be cut into 
the prism. If now we place such a prism into a “‘ kino-stereoscopic 
viewing device ” (Fig. 44) we can see the positives stereoscopically ; 





Fig. 44.—Kino-Stereoscopic Viewing Device. 


The light-cone on the left side, coming from the excentrically placed 
ocular “ OI,” is passed over the mirror “‘ M ”’ (forming part of a right- 
angle reflecting prism P), showing us the picture placed at the right 
side in “‘F2.” Supplementary lenses may be inserted anywhere in 
the single light-cones. The pictures are seen across each other’s light- 
path. Therefore, the eyes will see the two different pictures in the 
correct position, 7.e., in the right position to be amalgamated by the 
human sight nerves into one picture in relief. 

The positives obtained as above can also be projected on the 
screen ; in that case, one series, say the left, is projected through a 
green colour-filter, and the right through an orange-red one. The 
two pictures are projected together in preference, superposed or 
part superposed, which is effected with wedge prisms or wedge 
lenses placed in front, or at the back, of the projecting lens in a 
projector of the ordinary type, which has been altered to take films 
of double width. The stereoscopic effect is obtained when viewing 
with similarly coloured spectacles. I may say here that, in my 
opinion, those who think they will see stereoscopic pictures on the 
screen without such selective colour-filters will always be disappointed. 

The arrangement in Fig. 42 lends itself admirably to a modifica- 
tion. The light-cones have not necessarily to be formed on a level, 


116 COLOUR PHOTOGRAPHY. 


but can be placed one above the other as shown in “ kino-stereoscopic 
taking and viewing device’ (Fig. 45). Personally I have made no 
experiments on this line, but simply suggest that the working is 
correct. In that case the left side prism, with its base “O,”’ and the right 
side prism, with its base “‘ P,” form the two picture planes “ F1 ” and 
**F2,”’ one above the other, so that films of ordinary width can be used. 
When viewing the subjects in the instrument, the positive obtained on 
focussing plane “F1,” has to be shown through focussing plane ‘‘F2 ”’ 
in the other light-cone, and vice versa. Projection on to the screen can 
also be accomplished by the same instrument, or by a projector 
having a movement of two pictures. In the latter case the two 





WW CX WO WH. 
ame 
5 


a 


WHI 
mass 
NY 


Fig. 45.—Kino-Stereoscopic Taking and Viewing Device. 


pictures would be projected together with one lens, and a better 
super-position would be obtained with wedges, as explained before. 
Another method would be to use an ordinary projector with a standard 
movement, which should bring the red and green images, by per- 
sistence of vision, to the eyes, as stereoscopic pictures. In all cases 
selection by colour-filters comes into play; were they omitted a 
frightful flicker would be the only result. 

There is also the possibility of taking two pictures spaced on a 
film running horizontally, direct and without any reflecting device ; 
the superposition of the positives by the aid of wedges and colour 
filters can be done through the same instrument. The taking of 
two pictures at the eyes’ distance on two vertically running films 
has been tried already, but it proved a failure, because the corre- 
sponding pictures were so easily lost, nor did the inventors use 
selecting colour-filters. 

The above, I think, clearly sets out the basic principles of the 
subject of stereoscopic kinematography, and as a result many 
would-be patentees should be saved much misdirected trouble 
and labour. 


INDEX 


Abney, Patent of 

Absorption of Filters 

Absorption of Secondary Rays .. 
Absorption of Transmitted pea 
Acetic Acid, Use. of.. = : 
Acetone 

Acid Yellow 

Additive Light Projection .. 
Additive Method a 
Additive Primary Colours . 
Additive versus Subtractive 
Alcohol, Solubility of Dyes in 
Alkaline Bath : 

Alum Substratum, Effect of 
Amidol Developer § 

Ammonia for Washing Out Colours 
Ammonia in Sensitizing Solutions .. 
Ammoniated Fumigation 
Ammonium Nitrate 

Ammonium Picrate. : = 
Anomalism in Reflector Cameras | 
Arc Light 

Atmospheric Influences 
Autochrome ... Fan 

Azalin 


Balancing of Light Filters and Plates 
Barnard, Patent of. : 
Bathing Dry Plates 
Bennetto, Patent of 
Bichromate Sensitizing 
Bleaching Prints 

Blue Dyes 

Blue Filter 

Blue Printer 

Blue Toning 

Bromide Plates 

Brown, Theodore, Patent of 
Bromide Prints 

Butler, Patents of 


piled S7ase0s0m 7 5254073 


61e-81)- 08. 101 


61, 70, 75 


80 
-.99, 102 
65, 67, 68, 72, 104 


(12, 13,14, 48.39, 40,43, 46, 54 


97, 104 

sis 100 

eA Si 

69, Te iol O 

: 10.103 
100 

67 

aR 11 

38, ep 95, 96, 99 
9,13 


Cameras 2, 3, ge5..0,9,010,°12, 1316,18;520). 24, 26, 27,30, 34,38, 39.40, 


Calcium Tubes 
Camera Extension 


42, 46, 47, 48, 76, 83, 84, 86 
Sie 105 
44 


X1ii. 


INDEX. 


Camera Construction 
Canada Balsam 

Carbon Pigments 

Carbon Printing 

Carbon Transfer 

Celluloid Films ws 
Cementing Colour Filters ... 
Change of Light in ea: 
Chloroform : 

Chloride of Sodium . 
Chromoscope 

Chromogram ... 

Chromo- “Lithographic Colour Prints 
Cinematography in Colours 
Circular Distortion ... : 
Cleaning Negatives ... 
Cleaning Reflectors ... 
Collodion Films 

Collodion Plates 

Collodion Transfers ... 
Collotype Process 

Colour, Correct Reproduction 
Colour Fringes ioe 
Colour Enigmas : 
Colour Kinematography 
Colour Prints a 
Colour Records 

Colour Screens 

Colour Sensitizers 

Coloured Glasses 

Colouring of Chrome Prints 
Compensation Plate 
Compensators 
Compensations 


Compensation with Right Angle Prisms" 


Compensated Bennetto Camera 
Comparatives in Reflector Cameras 


Constructive Guide in Camera Making ... 


Constructive Block ... 
Copying 

Crags Ns FL Patent of vt 
Cross Form of Reflectors .. 
Curved Surfaces 

Cyanol 

Cyanin 

Cyan Print 


Dark Slides ene 
Dark Room Illumination ev 
Davidson, Patent of 
Degradation of Colours 
Dense Negatives 
Diaphragms 


XIV. 


PAGE 

.. 83, 86 

36;°37,/62 

O86 

46, 50, 88, 94, 103 

ie 106 

...92, 103 

=F 62 

77 

106 

aes oe A 100 
4.58) TOC aie 16, 472-52 
‘s a 8 
51 

110 

34 

81 

es 56 

“104, 106 

aoe 106 

106 

92 

69 

10, ‘24, 111 

x 49 

s 12 

10, 49, 52 

ak 69.76, 73 

57, 60, TO 27s 
6, 506,58, 6S. G52078 
3, 5, $26, 27-2p4e 
ce 4 98 
40, 84, 85 


9, 6 34, 37, 38, 40, 47, 48, 54, 84 


36, 37, 39, 40, 84, 86, 87 
vas ae 36 

40 

42 

83 

86 

des ie 93 

4, 5, 10, 46,753 

aie 10 

3a 34 

58, 65, 66, 68, 71, 123 cn 
58,65, 67 


INDEX. 


PAGE 
Diapositives ... ae ee wl oe a 92 
Developing Three- colour Negatives et es ae ase sd 80 
Direct Vision Camera on ets ae oe ths mi Safe 6 
Dispersing Prisms ... ee ask ad Me hea a ri 1 
Displacement of Focus oe oe mL ae ce he Le 41 
Distorting Reflected Picture ae sie re ie Pa <onido, 54 
PASTOLEON |. .,.', : ae oe we og as ... 40, 48 
Direct Reflection ... ne sie oe ee +8 54 
Double Reflections ... ti Bas oe Se 3 25, 21, 32 dig oA 
Double Compensation : oe see Fe ee 48 
Dover Street Studios, Patent of . Bis. Bes asks ne See eights! 
Dry plates for Colour Work Hh oe ae ae ep Oe Ol o2 
Drying of Bathed Plates aM sea oa? 7 OO, OS 
Dry plates, Colour Sensitiveness of Ordinary ace oes wpatO9, 1 1, 815 
Ducos du Hauron ... oe Ss ve ? Pie AGRO ee LOOAtO OS 
Dye Colours te ae 1th es ee Fe ees OS Ole 80 
Dyeing Filters Bk es ese ce ee se -_ es 61 
Eczema, Chemical ... =e san ee ay Ae: on M, 82 
Edwards, Patent of ahs ae i cae ae 9 
Eosine.. si ae we eg ae: 61, 65, 68, 69, CU i 
Electric ‘Light. ee Eas ee ote ai eS : ae 58 
Enlarged Negatives . eo Fe ae eA . 93 
MivEnrosine ... eat 5S) 700, G4> G5) 66, 69, 70, -71, “72, 16 fiviee cH 
Etching Half-tones a e hs co oP ae 91 
Meacentic Lens Centres... bie “S ote ries aoe oa 12 
Excentric Projection ate ae See oe a a A. ZA 
Excentric Stops pe re Bee i dc Het el nila o4 
Exterior Focus Plane re ae Bie e oa vee 25 
Exterior Prism Position .... ee ae ee + : “18, 110 
Exposure Se ; = Delt oe “55, 58, O07 G...1 04° 
Exposure Ratio of Filters . bs se ea fee eb Une at 
Exposure Frame, adjustable ae ee ae i ae i 93 
Films, Stripping fe ser 103 
Filters, Light—3, 7, 9, 10, 13, 16, 25, 21, ea: 39, Al, 43, 53, 54, 55, 100.00; 
TS See 
Filter Colours Ha a aha eo an he Rebels rei he yes 
Filter Arrangement... sea ae ok cas ane are ee 54 
Film Negatives ae ches ae ee ee te Ca ee aye 
Filter Yellow os shite aS me ‘Se ie Pea a 63 
Filter Red... ae ae » ie fo: ie ‘ee shee Tu 
Fixing Negatives ... she ae =e ae fas ie se 81 
Fixed Focus Camera : a a oe ae ae Ear LO eur 
Flaps for Multiple Exposures oe Hee ene ak i ae 43 
Flowers, Photographing .... RSL Pi, Be oe ae oe ae 78 
Fluoresceinate site 59 
Focus ae GO; 14, 18, 20, 25; 26, 27, 29, 34, an 40, 48, 54, 85, 87, 95, 


HOCUES.NE Pianes—6, peetieel el 4a), L021 24.25.2206, Ai 20 aU G4 OO. aly 
39, 40, 47, 48, 54, 55, 63,076,-83,-85.-86:687,. 88. 116 
Dees a ee san 70 


Gelatine, Coating Films and Plates with ie 5. me Se 97 


xXV 


INDEX. 


PAGE 

Gelatine, Coating Filters with ... sae = - Sa a 60 
Ghost Pictures usd pis ae ne Fe og 18; 19.26 
GreenaDyess 0 ee Zot ine ok 61, 70 
Green Filters a ee ee 55, 58, 61, 70, 71, “72, 73, COmto) 
Grey Printing Plate, “The are Sue fos 94 
Glass, Cleaning ea ae ie ae dss EB ¢ a ae 106 
Glass, Coloured fee Se is ee ‘ades a Pas 5. 495 57 
Glass, Ground Be eS Age ie ete =e we 49, 50 
Glass, Optical vas Heo ds ue ee ee 14, 26 
Glass, Parallel 55 re = ih hse om aoe 14, 21, oo (oan 
Glass, Plate ext i ve tah tg ae 60 
Glass, Platinized He 4 ae Es a at: aie 27, 43, 56 
Glass Reflector <3 uae ne, Be Sis st oa 14%) 27,29 
Glass, Silvered ao ea aca a ay ae « 2p Aiea 
Glass, Varnished ae na ee re or ee + 212 DO 
Half-Tone Screen ... aa ah ee noe ier 44, 91 
Hamburger & Coston Patent oy: set ee fe met. fn 34 
Hydrochloric CIC ae ‘ 23 n' as se me 101, 102 
Hydroquinone in Developer id ae Mer af fas ie 80 
Hypo My ae cas - os aa Te 81, 95, 101 
Illumination of Negatives ... 1 ae oe Pe ae ae 91 
Indirect. Tonine Process <2 ast =e a <6 i ae 100 
India-rubber Coating ee ses ae ae: en = 104, 106 
Inner Focus Plane ... See ie a oe ae ee oe 25 
Interior Prism Position oe a See aoe ae: a8 19 
Internal Reflections Se iy ae : 2 Ct) Die. aan 
Intensifying ... ae sae nee ie es! ae os 81, 95 
Iron Alum... * aie Sy. sa ae ait se tick 101 
Isochromatic Filter . ae bk: oh ies oe ak poe Tile 
Isochromatic Plate ... Be me 69 
Trestle es ae ae fad 5, 6, 8, 27, 33) 36, 37, “46, 47, 53, 86 
Jumeaux Process oe: os on rr Fes ads ey 99,7. Tie 
Keeping of Sensitized Plates site a mae 2 ae ; 68 
Kinematography, Colour ... be — cee ves ike 12, 110 
Kino-stereoscopy ... ‘an “ee sian oe ve: 2% ; 113 
Laboratory ... os ar ee ee Ese ee a. Ss 80 
Lantern Slides ie ee re ae Pea wg : ae 64 
Lantern Slides in Colour ... Mit ae = we a ‘ne 96 
Last for Camera Construction ... nee ee as Ef: ae 86 
Lee & Turner Patent ae i. Hos ss oe a a. 110 
Lenses 2, 5, 6, 10, 11, 12, 13,18, 19, 21; 23) 29) 3454236 eee 
Light Action in One-exposure Camera ... ier ee sie ve 46 
Light Action in Chromoscope ; A7 
Light Cone 7g; S2105 414207. 1G: 21, 23, 25, 29, 30, Os 37, 39, “AO, 43, “44, 83, 
be RS a Oe 

Light Filters, Making of ... a a iss den san 60 
Light Filters for Cinematography _ eA 1d 
Igeht Pilters, 327, Odeo Oe2oee7. a3: 39, 41, 43, 53, 54, 55, 57, 58, 60, 
73, Tose eo 


XVI. 


oh 


INDEX. 


Light Path 


Light Ray 2, 5, 6, 8, 18, 19, 20, 21, 22, 25, 26, 29, 46, 47, 52, 53, 54, 73, 83, 86 


Lumly, Patent of 
Lucas’ Process 


Magenta 
Magnesium Flash Illumination 
Maxwell : 

Methylene Blue 
Metol-Hydroquinone Developer 
Meyer, Patent of 

Mills Cinematograph Process 
Minus Colours 

Mirrors 


Naphthol Green : 
Negative Colour Records 


Genta bens’... 
Ocular Mirror 


pe 5.6.0 610,111% 


PAGE 
9, 10 


i 
92 


OO; 0 

38 

8 53 

To 

80 

10 

ae 110 

A 2: 52, Oye moo, aku 

pA lee 2Z, 26, 43, 45, 46, 48, 91 
Olsen eicaaed 

16, D0; 55, 69, 70, 713, 76, 87, 94, 97 


Lead ied MU de a i 
fen) 


One-Exposure Camera, 2, 4, 12, 18, 25, 26, 28, 29, or 38, 39, 43, “46, 54, 56, 58, 


One-Reflector Camera 
Optical Axis 

Optical Centre 
Optical Glass... 

Open Arc Light 
Orange Filters 
Orthochrome ... 


Panchromatic Plate 
Panorama-like Ganiiiiation 
Panoramic Effect 

Pack, Plate 

Parallax ag 

Parallel Plate Refraction 
Parallel Plate Reflection 
Parallel Plates ie 
Parallel Surfaces, Gusved ae 
Peripheric Projection 
Persistence of Vision 
Pfenninger, Patent of 
Photo-Chromoscope ... 
Picture Plane ; 
Picture Planes 

Pigmentary Colours... 

’ Pinachrome : 

Pinaverdol 

Plate Speeds .. 

Plates, Colour Sénsitive 


Plates for One- Exposure Cameras 


Platinized Glass 
Polarized Light Effects 


GS Liou soe. Ven ed 

13, 39, 40, 43, 46, 54, 58, 75, 83, 84, 86 
2b 24 

“1h, 22, 23, 29 

: Me 26 

fan 58 

Tie Os mice 

: 110 

O2p203,000,-00, O08eI U2 10,5 Lom Sumo 
a 22 

vi, 20; 22 

13, 41, 55 

12 

’ Hiss 

27, 25, 00,00 

41, 48, 60 

33 

23 

ms 116 

ie 38, 40 

8 

85 

: 4] 

: 2 ‘4, 49, DO a202 

58, 63, 66, TORT Te ell O 

63, 66, 70;-72 

die : Da 
oa 53, D0; 58, 65, PO wCnie 


INDEX. 


PAGE 
Pollock. Patenteo. . ay: Ae Pe cae Pes Ane aA 10 
Polychromide Printing Process: -...; 38 
Positives gee bien avi 41.47, 53, 73, 87, 88, ‘90, 92, 95, 96, 99, ‘101, Bs 
Positive Colour Records 45 id Opie 
Potassium Bromide . : a so) ae ed << on 101 
Potassium Carbonate? Use of ee —e os Bee ree a0 65 
Pressure Devices ... ey, ix = aes ie — PPS sit. | 
Predominant Hue ... 44h eM =e ates ae Sy we 49 
Primary Colours ae ae eee ca tee ee i Fees 
Printing Colours re ae a st ot he: 1, 49, 53, dBi cane 
Printing in Colour ... ae APs: ao aes = ie 49 
Printers’ Colours ee shes a fe Be. ee cea ma ff) 
Prisms ae .. 5,6, 10, 18, 19,°20; 21 2ak eee 37, Ae 114 
Prism Base Down Refraction a tt <2 <i BAY s 17 
Prism Base Down Reflection ci sae ee om <A ee ot 
Prism Base Up Refraction ee pas sae ie a des 17 
Prism Base Up Reflection te fe sad a cae ee 27 
Prism Separation... ie wee eo ais ag ce e 18 
Prismatic Dispersion a a we ee + ie Bn as Peo 
Process Faking = at ae ee = ee: 2a ae 90 
Redvers ee. ne ce ao iP ee ae is Se 70 
Red Printer ... net se is ee cote es are 70 
Red Printing Negative at re ie ia Por 87, 95, 103 
Red Prueciate ras oe nies ce Sed soe ae 100, 101 
Red Record ... me Pes aah Bak Soa ae ices 10. FSS 
Reducing Negatives : - 81 


Reflectors—2, 5,6, 9510; 12, 13. 14, 15, 16, 21, 22, 93, 25, 26, 27, 28, 29, 3032, 
33, 37, 38, 39; 40, 42) 54-50, Gaee 


Reflected Light ate oa ies 13, 25, 26, 27,29, 30,37, 4a, ae ee 
Reflected Picture ... ee $e Rs an goa te 
Reflected Rays ee aue mi a ax 25, 26; 27, 29, 306s 
Reflections, Incorrect ee an th ie 28 nsU 
Reflections, Internal oe 2 ce oe es Si 27, 33, 54 
Reflection, ordinary sa 2m mei ae at a2 i 25 
Reflector Box i ae ste Bek 3 3h oe ve 13 
Reflector Cameras ... : 42 
Reflector Filter ris: 14, 26, 27, hiss 35, aT: 39, AO, AA, 48, 54, a 59, 63, 88 
Reflectors, Curved Parallel : ce eee 
Refracted Picture ... fe ae ae Ane Ae a4 34,°38;> 46 
Refraction Distortion bee ; ae ae 34 
Refraction—5, 9, 13, 14, 17, 20, 25, 20, 27, 20088 32, 33" 34, 36, 37, 38, 40, 

48, 85, 86 
Refraction Compensator ... Fe oe mi bee ~ dnd; AX 
Refraction Defect ... : ie te fe, 16, 29, 33, 37, 44 
Refraction Through Parallel Plate er Sue Aes 14 
Refraction Filter... : oe sae hee ae “ek 26%" 
Retouching Positives =: a. ae: oe oe a bis 90 
Retouching Prints ... ze res ae a ee oe Weegee i S 
Reversed Negatives oe ee oe - 87,. 88, 91, 93. S57 97 
Reversing Prism ... sie Aon Lee ‘ak Ret ust ws 91 
Safelights Pe i sph ie sa Be v8 sae Jd 81 
XVIli. 


a Set ee 


——. ee ee 


INDEX. 


PAGE 
Scarlet Dyes + one ie 2, af sa sai Sa 61 
Scarlet Filter is os ae OY, seh oe ee ae 76 
Screens ee Aa ai ane oe me bap oe 644,807 
Screen, Distance ti Lap aa ae fa site ae an 44 
Screen, Opening a 4 * i = 13 5 ve 44 
soreen, Negatives... oe aes ae out he Ba 88, 90, 94 
Secondary Light Action ... are ite ee 14 ee oe za 
Secondary Picture ... an Ae aot ire sa con eOr ane Ta00 
Secondary Reflections me tan ee es Be ae ae 26 
Secondary Focussing Plane Coen a. i ue ee ay 27 
Separation Camera ... ay As aay ie ae 13 
Self-Compensating Reflection Filter ES 100; we Re 3 13 
Self-Compensating Reflector ms = aed pea " 38 
Sensitizing Dyes an tim a, ey cra Pe 58, 63 
Sensitizing with Bi- chromate he oe te tee ior 97, 104 
Sensitizing Carbon. Tissue ... oe ie Ye tn bee sisis 104 
Shepherd, Patent of ; oe eee nn ord oh ee 7 
Shrinkage of Celluloid Films oy “ee oe nl te at 92 
Signal Green . : 57 a a ae = sfc ba 
Silvered Glass _ fe es ie a sa oak sae be 27 
Single Compensation oe. us Se ake oe es oe 48 
Sight Filters ... es tee ee 5 ae ote Be 59 
Sight Transposing Prism ... at oa sh ae A ae 114 
Size of Images ia ve ne Sn Se a ne - 88 
Sky Screening re oe i uae aoe! ,142, 44 
Smith, Albert, Process of . Fi at a ee | 
Soda Carbonate, for Washing- -out ‘Colours ie eae O00 ta 102 
Soda Carbonate in Bleaching Solution ... soy ae vn oe 100 
Spectral Dispersions ant ie — ee ate Te ANS 26 
Spectroscope, Artificial ay ie oT a sie : Te 
Spectrum, Colours. ... Ae me Ah ae te 50, 52, 53, 75, 96 
Stereoscopic Camera Ee Fy a Sa ae Pd lS 
Stereoscopic Difference ¥e 4) x a ae 2 20, 23, 24, 111 
eereoscopic Effect... an tee ad sat lO dt, 204115 
Stereoscopic Reflecting Systems fe ion ve a ee S58 11 
Stereoscopic Viewing Device 7B ae hs ae cas Kee 36 
Stereoscopy, Kino. ... oe “is Hee r je ay gn 110 
Stop, .hree-spaced ... te es ie oe oe es wes 12 
SSLODS >. '= a er oe ap es my ms is 44 
Stripping Films ee ay 99, 103 
Subtractive Method eel; 4, 4, 8, “ies 16, 20, 24, 39, 46, DUD Ao Ler 
Subtractive Colour Camera Ss Se 13 
Subtractive Light Projection oes wee ny. o. =e gs 46 
Subtractive Primaries op ae ed ra . TE on 52 
Sulphuric Acid ay a ye ree ie oe as O77 101 
Supplementary Lenses ve a. be ree a ee ae we 
Tare zine § —... eg ee za ee hae 61, 104 
Temperature of Laboratory i ait re she ee es 80 
Tension by a Gelatine Surface ... fi ee a oe mae 35 
Testing for Size of Images ca ain nce or a xe 87 
Theoretical Light Filters ... re pes i ao Py are 57 
Theoretical Primaries ee iis ate oe ate th fied 52 

1 


INDEX. 


Three-Colour Blocks a nae oe e. ee ie eas 46 
Three-Colour Prints es ae oy ons we eae 2.40 ok 
Three-focus Instrument ... oh er = fae oa; aoe 48 
Toned Bromide Prints ce ave oe ae eo 88, 95, 96, 99 
Transmitting Reflector th sie ke ae ae is 26, 43, 55 
Transmitted Light ... Arf: ase Rs Res aes is Pe be 
Transmitted Pictures ae ans Poe ats iG ‘ 21a 
Transparencies eae ae Ra sie & ee 49, 73. 93, 96 
Transparent Colours ee “ey es Le 94 
Transparent Reflectors be ee? ae ean 2, Gy 6, 8, 10, 26, 30 
Trio of Lenses ae a ie + des i Oe V2 
Triple Camera ae M & ace Bx: Bone a 7, 8, 11, “02; Al has 
Turnbull’s Blue 40 nae ae ee ee 5 eed ... 96, 99 
Two-picture Focus.... - ae oe ue ee oe woe h BIEZS 
Two-reflector Cameras a att so e? on me ... 47, 86 


Unsharpness of Image Sey ae a Sak a a oe 29 
Uranin Siok ane re af sa ea ie ono) DOR OF ies 
Uranoty per. an or a es ae ne ve Fae 88 


Varnishing Colour Filters ... AS ae fe Lee sau ae 60 
Verdol ; oe + ne ee. jst ee a3 65 
Vertical Refraction A ae ae od a a ne ee oa 14 
Viewing Instruments ee ee ane 4, 8, 47, 48 
Viewing of Colours by Reflected ‘Light A ae oe afc pe. 99 
Violet Crystals ee wae see os ae “2 Leen 
Violet Filter ... Se ole iiss ae ae Te ott ae 75 


Washing-out of Colours... Ss ae ie mie ee: el 98 
Wedge Prism Compensator ea ia sa es SY 
Wedge Prisms sig me se wes ~eg ipa 18, 20, 27, 37, 115 
Whites Patentyot.i..: ee ae ce " we : 7 


VOVORN CEG 9 es nat ar aise ee ue ~~ ee ae 70 


Yellow Dyes... ee ree a ae owe Fes ce Olseg0 
Yellow Filter... Aw uae ie ate ae. mat O23 76 
Yellow Print a w2 cae coi oe oe 69, 94, “103, 109 
Yellow Record : fz: Ge es ae a 69. 72,383 
Yellow Reflector Filter we Ley ae aa ae ee ae 32 


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